contrib/bc: merge from vendor release 6.2.2

[FreeBSD/FreeBSD.git] / sys / netinet / tcp_subr.c

/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (c) 1982, 1986, 1988, 1990, 1993, 1995
 *      The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)tcp_subr.c  8.2 (Berkeley) 5/24/95
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");

#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_ipsec.h"
#include "opt_kern_tls.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/arb.h>
#include <sys/callout.h>
#include <sys/eventhandler.h>
#ifdef TCP_HHOOK
#include <sys/hhook.h>
#endif
#include <sys/kernel.h>
#ifdef TCP_HHOOK
#include <sys/khelp.h>
#endif
#ifdef KERN_TLS
#include <sys/ktls.h>
#endif
#include <sys/qmath.h>
#include <sys/stats.h>
#include <sys/sysctl.h>
#include <sys/jail.h>
#include <sys/malloc.h>
#include <sys/refcount.h>
#include <sys/mbuf.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/sdt.h>
#include <sys/socket.h>
#include <sys/socketvar.h>
#include <sys/protosw.h>
#include <sys/random.h>

#include <vm/uma.h>

#include <net/route.h>
#include <net/route/nhop.h>
#include <net/if.h>
#include <net/if_var.h>
#include <net/vnet.h>

#include <netinet/in.h>
#include <netinet/in_fib.h>
#include <netinet/in_kdtrace.h>
#include <netinet/in_pcb.h>
#include <netinet/in_systm.h>
#include <netinet/in_var.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netinet/ip_var.h>
#ifdef INET6
#include <netinet/icmp6.h>
#include <netinet/ip6.h>
#include <netinet6/in6_fib.h>
#include <netinet6/in6_pcb.h>
#include <netinet6/ip6_var.h>
#include <netinet6/scope6_var.h>
#include <netinet6/nd6.h>
#endif

#include <netinet/tcp.h>
#ifdef INVARIANTS
#define TCPSTATES
#endif
#include <netinet/tcp_fsm.h>
#include <netinet/tcp_seq.h>
#include <netinet/tcp_timer.h>
#include <netinet/tcp_var.h>
#include <netinet/tcp_ecn.h>
#include <netinet/tcp_log_buf.h>
#include <netinet/tcp_syncache.h>
#include <netinet/tcp_hpts.h>
#include <netinet/cc/cc.h>
#include <netinet/tcpip.h>
#include <netinet/tcp_fastopen.h>
#ifdef TCPPCAP
#include <netinet/tcp_pcap.h>
#endif
#ifdef TCP_OFFLOAD
#include <netinet/tcp_offload.h>
#endif
#include <netinet/udp.h>
#include <netinet/udp_var.h>
#ifdef INET6
#include <netinet6/tcp6_var.h>
#endif

#include <netipsec/ipsec_support.h>

#include <machine/in_cksum.h>
#include <crypto/siphash/siphash.h>

#include <security/mac/mac_framework.h>

#ifdef INET6
static ip6proto_ctlinput_t tcp6_ctlinput;
static udp_tun_icmp_t tcp6_ctlinput_viaudp;
#endif

VNET_DEFINE(int, tcp_mssdflt) = TCP_MSS;
#ifdef INET6
VNET_DEFINE(int, tcp_v6mssdflt) = TCP6_MSS;
#endif

#ifdef NETFLIX_EXP_DETECTION
/*  Sack attack detection thresholds and such */
SYSCTL_NODE(_net_inet_tcp, OID_AUTO, sack_attack,
    CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "Sack Attack detection thresholds");
int32_t tcp_force_detection = 0;
SYSCTL_INT(_net_inet_tcp_sack_attack, OID_AUTO, force_detection,
    CTLFLAG_RW,
    &tcp_force_detection, 0,
    "Do we force detection even if the INP has it off?");
int32_t tcp_sack_to_ack_thresh = 700;   /* 70 % */
SYSCTL_INT(_net_inet_tcp_sack_attack, OID_AUTO, sack_to_ack_thresh,
    CTLFLAG_RW,
    &tcp_sack_to_ack_thresh, 700,
    "Percentage of sacks to acks we must see above (10.1 percent is 101)?");
int32_t tcp_sack_to_move_thresh = 600;  /* 60 % */
SYSCTL_INT(_net_inet_tcp_sack_attack, OID_AUTO, move_thresh,
    CTLFLAG_RW,
    &tcp_sack_to_move_thresh, 600,
    "Percentage of sack moves we must see above (10.1 percent is 101)");
int32_t tcp_restoral_thresh = 650;      /* 65 % (sack:2:ack -5%) */
SYSCTL_INT(_net_inet_tcp_sack_attack, OID_AUTO, restore_thresh,
    CTLFLAG_RW,
    &tcp_restoral_thresh, 550,
    "Percentage of sack to ack percentage we must see below to restore(10.1 percent is 101)");
int32_t tcp_sad_decay_val = 800;
SYSCTL_INT(_net_inet_tcp_sack_attack, OID_AUTO, decay_per,
    CTLFLAG_RW,
    &tcp_sad_decay_val, 800,
    "The decay percentage (10.1 percent equals 101 )");
int32_t tcp_map_minimum = 500;
SYSCTL_INT(_net_inet_tcp_sack_attack, OID_AUTO, nummaps,
    CTLFLAG_RW,
    &tcp_map_minimum, 500,
    "Number of Map enteries before we start detection");
int32_t tcp_attack_on_turns_on_logging = 0;
SYSCTL_INT(_net_inet_tcp_sack_attack, OID_AUTO, attacks_logged,
    CTLFLAG_RW,
    &tcp_attack_on_turns_on_logging, 0,
   "When we have a positive hit on attack, do we turn on logging?");
int32_t tcp_sad_pacing_interval = 2000;
SYSCTL_INT(_net_inet_tcp_sack_attack, OID_AUTO, sad_pacing_int,
    CTLFLAG_RW,
    &tcp_sad_pacing_interval, 2000,
    "What is the minimum pacing interval for a classified attacker?");

int32_t tcp_sad_low_pps = 100;
SYSCTL_INT(_net_inet_tcp_sack_attack, OID_AUTO, sad_low_pps,
    CTLFLAG_RW,
    &tcp_sad_low_pps, 100,
    "What is the input pps that below which we do not decay?");
#endif
uint32_t tcp_ack_war_time_window = 1000;
SYSCTL_UINT(_net_inet_tcp, OID_AUTO, ack_war_timewindow,
    CTLFLAG_RW,
    &tcp_ack_war_time_window, 1000,
   "If the tcp_stack does ack-war prevention how many milliseconds are in its time window?");
uint32_t tcp_ack_war_cnt = 5;
SYSCTL_UINT(_net_inet_tcp, OID_AUTO, ack_war_cnt,
    CTLFLAG_RW,
    &tcp_ack_war_cnt, 5,
   "If the tcp_stack does ack-war prevention how many acks can be sent in its time window?");

struct rwlock tcp_function_lock;

static int
sysctl_net_inet_tcp_mss_check(SYSCTL_HANDLER_ARGS)
{
        int error, new;

        new = V_tcp_mssdflt;
        error = sysctl_handle_int(oidp, &new, 0, req);
        if (error == 0 && req->newptr) {
                if (new < TCP_MINMSS)
                        error = EINVAL;
                else
                        V_tcp_mssdflt = new;
        }
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, TCPCTL_MSSDFLT, mssdflt,
    CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
    &VNET_NAME(tcp_mssdflt), 0, &sysctl_net_inet_tcp_mss_check, "I",
    "Default TCP Maximum Segment Size");

#ifdef INET6
static int
sysctl_net_inet_tcp_mss_v6_check(SYSCTL_HANDLER_ARGS)
{
        int error, new;

        new = V_tcp_v6mssdflt;
        error = sysctl_handle_int(oidp, &new, 0, req);
        if (error == 0 && req->newptr) {
                if (new < TCP_MINMSS)
                        error = EINVAL;
                else
                        V_tcp_v6mssdflt = new;
        }
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, TCPCTL_V6MSSDFLT, v6mssdflt,
    CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
    &VNET_NAME(tcp_v6mssdflt), 0, &sysctl_net_inet_tcp_mss_v6_check, "I",
   "Default TCP Maximum Segment Size for IPv6");
#endif /* INET6 */

/*
 * Minimum MSS we accept and use. This prevents DoS attacks where
 * we are forced to a ridiculous low MSS like 20 and send hundreds
 * of packets instead of one. The effect scales with the available
 * bandwidth and quickly saturates the CPU and network interface
 * with packet generation and sending. Set to zero to disable MINMSS
 * checking. This setting prevents us from sending too small packets.
 */
VNET_DEFINE(int, tcp_minmss) = TCP_MINMSS;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, minmss, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_minmss), 0,
    "Minimum TCP Maximum Segment Size");

VNET_DEFINE(int, tcp_do_rfc1323) = 1;
SYSCTL_INT(_net_inet_tcp, TCPCTL_DO_RFC1323, rfc1323, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(tcp_do_rfc1323), 0,
    "Enable rfc1323 (high performance TCP) extensions");

/*
 * As of June 2021, several TCP stacks violate RFC 7323 from September 2014.
 * Some stacks negotiate TS, but never send them after connection setup. Some
 * stacks negotiate TS, but don't send them when sending keep-alive segments.
 * These include modern widely deployed TCP stacks.
 * Therefore tolerating violations for now...
 */
VNET_DEFINE(int, tcp_tolerate_missing_ts) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tolerate_missing_ts, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(tcp_tolerate_missing_ts), 0,
    "Tolerate missing TCP timestamps");

VNET_DEFINE(int, tcp_ts_offset_per_conn) = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, ts_offset_per_conn, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(tcp_ts_offset_per_conn), 0,
    "Initialize TCP timestamps per connection instead of per host pair");

/* How many connections are pacing */
static volatile uint32_t number_of_tcp_connections_pacing = 0;
static uint32_t shadow_num_connections = 0;

static int tcp_pacing_limit = 10000;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, pacing_limit, CTLFLAG_RW,
    &tcp_pacing_limit, 1000,
    "If the TCP stack does pacing, is there a limit (-1 = no, 0 = no pacing N = number of connections)");

SYSCTL_UINT(_net_inet_tcp, OID_AUTO, pacing_count, CTLFLAG_RD,
    &shadow_num_connections, 0, "Number of TCP connections being paced");

static int      tcp_log_debug = 0;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, log_debug, CTLFLAG_RW,
    &tcp_log_debug, 0, "Log errors caused by incoming TCP segments");

static int      tcp_tcbhashsize;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, tcbhashsize, CTLFLAG_RDTUN | CTLFLAG_NOFETCH,
    &tcp_tcbhashsize, 0, "Size of TCP control-block hashtable");

static int      do_tcpdrain = 1;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, do_tcpdrain, CTLFLAG_RW, &do_tcpdrain, 0,
    "Enable tcp_drain routine for extra help when low on mbufs");

SYSCTL_UINT(_net_inet_tcp, OID_AUTO, pcbcount, CTLFLAG_VNET | CTLFLAG_RD,
    &VNET_NAME(tcbinfo.ipi_count), 0, "Number of active PCBs");

VNET_DEFINE_STATIC(int, icmp_may_rst) = 1;
#define V_icmp_may_rst                  VNET(icmp_may_rst)
SYSCTL_INT(_net_inet_tcp, OID_AUTO, icmp_may_rst, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(icmp_may_rst), 0,
    "Certain ICMP unreachable messages may abort connections in SYN_SENT");

VNET_DEFINE_STATIC(int, tcp_isn_reseed_interval) = 0;
#define V_tcp_isn_reseed_interval       VNET(tcp_isn_reseed_interval)
SYSCTL_INT(_net_inet_tcp, OID_AUTO, isn_reseed_interval, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(tcp_isn_reseed_interval), 0,
    "Seconds between reseeding of ISN secret");

static int      tcp_soreceive_stream;
SYSCTL_INT(_net_inet_tcp, OID_AUTO, soreceive_stream, CTLFLAG_RDTUN,
    &tcp_soreceive_stream, 0, "Using soreceive_stream for TCP sockets");

VNET_DEFINE(uma_zone_t, sack_hole_zone);
#define V_sack_hole_zone                VNET(sack_hole_zone)
VNET_DEFINE(uint32_t, tcp_map_entries_limit) = 0;       /* unlimited */
static int
sysctl_net_inet_tcp_map_limit_check(SYSCTL_HANDLER_ARGS)
{
        int error;
        uint32_t new;

        new = V_tcp_map_entries_limit;
        error = sysctl_handle_int(oidp, &new, 0, req);
        if (error == 0 && req->newptr) {
                /* only allow "0" and value > minimum */
                if (new > 0 && new < TCP_MIN_MAP_ENTRIES_LIMIT)
                        error = EINVAL;
                else
                        V_tcp_map_entries_limit = new;
        }
        return (error);
}
SYSCTL_PROC(_net_inet_tcp, OID_AUTO, map_limit,
    CTLFLAG_VNET | CTLTYPE_UINT | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
    &VNET_NAME(tcp_map_entries_limit), 0,
    &sysctl_net_inet_tcp_map_limit_check, "IU",
    "Total sendmap entries limit");

VNET_DEFINE(uint32_t, tcp_map_split_limit) = 0; /* unlimited */
SYSCTL_UINT(_net_inet_tcp, OID_AUTO, split_limit, CTLFLAG_VNET | CTLFLAG_RW,
     &VNET_NAME(tcp_map_split_limit), 0,
    "Total sendmap split entries limit");

#ifdef TCP_HHOOK
VNET_DEFINE(struct hhook_head *, tcp_hhh[HHOOK_TCP_LAST+1]);
#endif

#define TS_OFFSET_SECRET_LENGTH SIPHASH_KEY_LENGTH
VNET_DEFINE_STATIC(u_char, ts_offset_secret[TS_OFFSET_SECRET_LENGTH]);
#define V_ts_offset_secret      VNET(ts_offset_secret)

static int      tcp_default_fb_init(struct tcpcb *tp);
static void     tcp_default_fb_fini(struct tcpcb *tp, int tcb_is_purged);
static int      tcp_default_handoff_ok(struct tcpcb *tp);
static struct inpcb *tcp_notify(struct inpcb *, int);
static struct inpcb *tcp_mtudisc_notify(struct inpcb *, int);
static struct inpcb *tcp_mtudisc(struct inpcb *, int);
static struct inpcb *tcp_drop_syn_sent(struct inpcb *, int);
static char *   tcp_log_addr(struct in_conninfo *inc, struct tcphdr *th,
                    const void *ip4hdr, const void *ip6hdr);
static ipproto_ctlinput_t       tcp_ctlinput;
static udp_tun_icmp_t           tcp_ctlinput_viaudp;

static struct tcp_function_block tcp_def_funcblk = {
        .tfb_tcp_block_name = "freebsd",
        .tfb_tcp_output = tcp_default_output,
        .tfb_tcp_do_segment = tcp_do_segment,
        .tfb_tcp_ctloutput = tcp_default_ctloutput,
        .tfb_tcp_handoff_ok = tcp_default_handoff_ok,
        .tfb_tcp_fb_init = tcp_default_fb_init,
        .tfb_tcp_fb_fini = tcp_default_fb_fini,
};

static int tcp_fb_cnt = 0;
struct tcp_funchead t_functions;
static struct tcp_function_block *tcp_func_set_ptr = &tcp_def_funcblk;

void
tcp_record_dsack(struct tcpcb *tp, tcp_seq start, tcp_seq end, int tlp)
{
        TCPSTAT_INC(tcps_dsack_count);
        tp->t_dsack_pack++;
        if (tlp == 0) {
                if (SEQ_GT(end, start)) {
                        tp->t_dsack_bytes += (end - start);
                        TCPSTAT_ADD(tcps_dsack_bytes, (end - start));
                } else {
                        tp->t_dsack_tlp_bytes += (start - end);
                        TCPSTAT_ADD(tcps_dsack_bytes, (start - end));
                }
        } else {
                if (SEQ_GT(end, start)) {
                        tp->t_dsack_bytes += (end - start);
                        TCPSTAT_ADD(tcps_dsack_tlp_bytes, (end - start));
                } else {
                        tp->t_dsack_tlp_bytes += (start - end);
                        TCPSTAT_ADD(tcps_dsack_tlp_bytes, (start - end));
                }
        }
}

static struct tcp_function_block *
find_tcp_functions_locked(struct tcp_function_set *fs)
{
        struct tcp_function *f;
        struct tcp_function_block *blk=NULL;

        TAILQ_FOREACH(f, &t_functions, tf_next) {
                if (strcmp(f->tf_name, fs->function_set_name) == 0) {
                        blk = f->tf_fb;
                        break;
                }
        }
        return(blk);
}

static struct tcp_function_block *
find_tcp_fb_locked(struct tcp_function_block *blk, struct tcp_function **s)
{
        struct tcp_function_block *rblk=NULL;
        struct tcp_function *f;

        TAILQ_FOREACH(f, &t_functions, tf_next) {
                if (f->tf_fb == blk) {
                        rblk = blk;
                        if (s) {
                                *s = f;
                        }
                        break;
                }
        }
        return (rblk);
}

struct tcp_function_block *
find_and_ref_tcp_functions(struct tcp_function_set *fs)
{
        struct tcp_function_block *blk;

        rw_rlock(&tcp_function_lock);
        blk = find_tcp_functions_locked(fs);
        if (blk)
                refcount_acquire(&blk->tfb_refcnt);
        rw_runlock(&tcp_function_lock);
        return(blk);
}

struct tcp_function_block *
find_and_ref_tcp_fb(struct tcp_function_block *blk)
{
        struct tcp_function_block *rblk;

        rw_rlock(&tcp_function_lock);
        rblk = find_tcp_fb_locked(blk, NULL);
        if (rblk)
                refcount_acquire(&rblk->tfb_refcnt);
        rw_runlock(&tcp_function_lock);
        return(rblk);
}

/* Find a matching alias for the given tcp_function_block. */
int
find_tcp_function_alias(struct tcp_function_block *blk,
    struct tcp_function_set *fs)
{
        struct tcp_function *f;
        int found;

        found = 0;
        rw_rlock(&tcp_function_lock);
        TAILQ_FOREACH(f, &t_functions, tf_next) {
                if ((f->tf_fb == blk) &&
                    (strncmp(f->tf_name, blk->tfb_tcp_block_name,
                        TCP_FUNCTION_NAME_LEN_MAX) != 0)) {
                        /* Matching function block with different name. */
                        strncpy(fs->function_set_name, f->tf_name,
                            TCP_FUNCTION_NAME_LEN_MAX);
                        found = 1;
                        break;
                }
        }
        /* Null terminate the string appropriately. */
        if (found) {
                fs->function_set_name[TCP_FUNCTION_NAME_LEN_MAX - 1] = '\0';
        } else {
                fs->function_set_name[0] = '\0';
        }
        rw_runlock(&tcp_function_lock);
        return (found);
}

static struct tcp_function_block *
find_and_ref_tcp_default_fb(void)
{
        struct tcp_function_block *rblk;

        rw_rlock(&tcp_function_lock);
        rblk = tcp_func_set_ptr;
        refcount_acquire(&rblk->tfb_refcnt);
        rw_runlock(&tcp_function_lock);
        return (rblk);
}

void
tcp_switch_back_to_default(struct tcpcb *tp)
{
        struct tcp_function_block *tfb;

        KASSERT(tp->t_fb != &tcp_def_funcblk,
            ("%s: called by the built-in default stack", __func__));

        /*
         * Release the old stack. This function will either find a new one
         * or panic.
         */
        if (tp->t_fb->tfb_tcp_fb_fini != NULL)
                (*tp->t_fb->tfb_tcp_fb_fini)(tp, 0);
        refcount_release(&tp->t_fb->tfb_refcnt);

        /*
         * Now, we'll find a new function block to use.
         * Start by trying the current user-selected
         * default, unless this stack is the user-selected
         * default.
         */
        tfb = find_and_ref_tcp_default_fb();
        if (tfb == tp->t_fb) {
                refcount_release(&tfb->tfb_refcnt);
                tfb = NULL;
        }
        /* Does the stack accept this connection? */
        if (tfb != NULL && tfb->tfb_tcp_handoff_ok != NULL &&
            (*tfb->tfb_tcp_handoff_ok)(tp)) {
                refcount_release(&tfb->tfb_refcnt);
                tfb = NULL;
        }
        /* Try to use that stack. */
        if (tfb != NULL) {
                /* Initialize the new stack. If it succeeds, we are done. */
                tp->t_fb = tfb;
                if (tp->t_fb->tfb_tcp_fb_init == NULL ||
                    (*tp->t_fb->tfb_tcp_fb_init)(tp) == 0)
                        return;

                /*
                 * Initialization failed. Release the reference count on
                 * the stack.
                 */
                refcount_release(&tfb->tfb_refcnt);
        }

        /*
         * If that wasn't feasible, use the built-in default
         * stack which is not allowed to reject anyone.
         */
        tfb = find_and_ref_tcp_fb(&tcp_def_funcblk);
        if (tfb == NULL) {
                /* there always should be a default */
                panic("Can't refer to tcp_def_funcblk");
        }
        if (tfb->tfb_tcp_handoff_ok != NULL) {
                if ((*tfb->tfb_tcp_handoff_ok) (tp)) {
                        /* The default stack cannot say no */
                        panic("Default stack rejects a new session?");
                }
        }
        tp->t_fb = tfb;
        if (tp->t_fb->tfb_tcp_fb_init != NULL &&
            (*tp->t_fb->tfb_tcp_fb_init)(tp)) {
                /* The default stack cannot fail */
                panic("Default stack initialization failed");
        }
}

static bool
tcp_recv_udp_tunneled_packet(struct mbuf *m, int off, struct inpcb *inp,
    const struct sockaddr *sa, void *ctx)
{
        struct ip *iph;
#ifdef INET6
        struct ip6_hdr *ip6;
#endif
        struct udphdr *uh;
        struct tcphdr *th;
        int thlen;
        uint16_t port;

        TCPSTAT_INC(tcps_tunneled_pkts);
        if ((m->m_flags & M_PKTHDR) == 0) {
                /* Can't handle one that is not a pkt hdr */
                TCPSTAT_INC(tcps_tunneled_errs);
                goto out;
        }
        thlen = sizeof(struct tcphdr);
        if (m->m_len < off + sizeof(struct udphdr) + thlen &&
            (m =  m_pullup(m, off + sizeof(struct udphdr) + thlen)) == NULL) {
                TCPSTAT_INC(tcps_tunneled_errs);
                goto out;
        }
        iph = mtod(m, struct ip *);
        uh = (struct udphdr *)((caddr_t)iph + off);
        th = (struct tcphdr *)(uh + 1);
        thlen = th->th_off << 2;
        if (m->m_len < off + sizeof(struct udphdr) + thlen) {
                m =  m_pullup(m, off + sizeof(struct udphdr) + thlen);
                if (m == NULL) {
                        TCPSTAT_INC(tcps_tunneled_errs);
                        goto out;
                } else {
                        iph = mtod(m, struct ip *);
                        uh = (struct udphdr *)((caddr_t)iph + off);
                        th = (struct tcphdr *)(uh + 1);
                }
        }
        m->m_pkthdr.tcp_tun_port = port = uh->uh_sport;
        bcopy(th, uh, m->m_len - off);
        m->m_len -= sizeof(struct udphdr);
        m->m_pkthdr.len -= sizeof(struct udphdr);
        /*
         * We use the same algorithm for
         * both UDP and TCP for c-sum. So
         * the code in tcp_input will skip
         * the checksum. So we do nothing
         * with the flag (m->m_pkthdr.csum_flags).
         */
        switch (iph->ip_v) {
#ifdef INET
        case IPVERSION:
                iph->ip_len = htons(ntohs(iph->ip_len) - sizeof(struct udphdr));
                tcp_input_with_port(&m, &off, IPPROTO_TCP, port);
                break;
#endif
#ifdef INET6
        case IPV6_VERSION >> 4:
                ip6 = mtod(m, struct ip6_hdr *);
                ip6->ip6_plen = htons(ntohs(ip6->ip6_plen) - sizeof(struct udphdr));
                tcp6_input_with_port(&m, &off, IPPROTO_TCP, port);
                break;
#endif
        default:
                goto out;
                break;
        }
        return (true);
out:
        m_freem(m);

        return (true);
}

static int
sysctl_net_inet_default_tcp_functions(SYSCTL_HANDLER_ARGS)
{
        int error=ENOENT;
        struct tcp_function_set fs;
        struct tcp_function_block *blk;

        memset(&fs, 0, sizeof(fs));
        rw_rlock(&tcp_function_lock);
        blk = find_tcp_fb_locked(tcp_func_set_ptr, NULL);
        if (blk) {
                /* Found him */
                strcpy(fs.function_set_name, blk->tfb_tcp_block_name);
                fs.pcbcnt = blk->tfb_refcnt;
        }
        rw_runlock(&tcp_function_lock);
        error = sysctl_handle_string(oidp, fs.function_set_name,
                                     sizeof(fs.function_set_name), req);

        /* Check for error or no change */
        if (error != 0 || req->newptr == NULL)
                return(error);

        rw_wlock(&tcp_function_lock);
        blk = find_tcp_functions_locked(&fs);
        if ((blk == NULL) ||
            (blk->tfb_flags & TCP_FUNC_BEING_REMOVED)) {
                error = ENOENT;
                goto done;
        }
        tcp_func_set_ptr = blk;
done:
        rw_wunlock(&tcp_function_lock);
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, functions_default,
    CTLTYPE_STRING | CTLFLAG_RW | CTLFLAG_NEEDGIANT,
    NULL, 0, sysctl_net_inet_default_tcp_functions, "A",
    "Set/get the default TCP functions");

static int
sysctl_net_inet_list_available(SYSCTL_HANDLER_ARGS)
{
        int error, cnt, linesz;
        struct tcp_function *f;
        char *buffer, *cp;
        size_t bufsz, outsz;
        bool alias;

        cnt = 0;
        rw_rlock(&tcp_function_lock);
        TAILQ_FOREACH(f, &t_functions, tf_next) {
                cnt++;
        }
        rw_runlock(&tcp_function_lock);

        bufsz = (cnt+2) * ((TCP_FUNCTION_NAME_LEN_MAX * 2) + 13) + 1;
        buffer = malloc(bufsz, M_TEMP, M_WAITOK);

        error = 0;
        cp = buffer;

        linesz = snprintf(cp, bufsz, "\n%-32s%c %-32s %s\n", "Stack", 'D',
            "Alias", "PCB count");
        cp += linesz;
        bufsz -= linesz;
        outsz = linesz;

        rw_rlock(&tcp_function_lock);
        TAILQ_FOREACH(f, &t_functions, tf_next) {
                alias = (f->tf_name != f->tf_fb->tfb_tcp_block_name);
                linesz = snprintf(cp, bufsz, "%-32s%c %-32s %u\n",
                    f->tf_fb->tfb_tcp_block_name,
                    (f->tf_fb == tcp_func_set_ptr) ? '*' : ' ',
                    alias ? f->tf_name : "-",
                    f->tf_fb->tfb_refcnt);
                if (linesz >= bufsz) {
                        error = EOVERFLOW;
                        break;
                }
                cp += linesz;
                bufsz -= linesz;
                outsz += linesz;
        }
        rw_runlock(&tcp_function_lock);
        if (error == 0)
                error = sysctl_handle_string(oidp, buffer, outsz + 1, req);
        free(buffer, M_TEMP);
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, functions_available,
    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_NEEDGIANT,
    NULL, 0, sysctl_net_inet_list_available, "A",
    "list available TCP Function sets");

VNET_DEFINE(int, tcp_udp_tunneling_port) = TCP_TUNNELING_PORT_DEFAULT;

#ifdef INET
VNET_DEFINE(struct socket *, udp4_tun_socket) = NULL;
#define V_udp4_tun_socket       VNET(udp4_tun_socket)
#endif
#ifdef INET6
VNET_DEFINE(struct socket *, udp6_tun_socket) = NULL;
#define V_udp6_tun_socket       VNET(udp6_tun_socket)
#endif

static struct sx tcpoudp_lock;

static void
tcp_over_udp_stop(void)
{

        sx_assert(&tcpoudp_lock, SA_XLOCKED);

#ifdef INET
        if (V_udp4_tun_socket != NULL) {
                soclose(V_udp4_tun_socket);
                V_udp4_tun_socket = NULL;
        }
#endif
#ifdef INET6
        if (V_udp6_tun_socket != NULL) {
                soclose(V_udp6_tun_socket);
                V_udp6_tun_socket = NULL;
        }
#endif
}

static int
tcp_over_udp_start(void)
{
        uint16_t port;
        int ret;
#ifdef INET
        struct sockaddr_in sin;
#endif
#ifdef INET6
        struct sockaddr_in6 sin6;
#endif

        sx_assert(&tcpoudp_lock, SA_XLOCKED);

        port = V_tcp_udp_tunneling_port;
        if (ntohs(port) == 0) {
                /* Must have a port set */
                return (EINVAL);
        }
#ifdef INET
        if (V_udp4_tun_socket != NULL) {
                /* Already running -- must stop first */
                return (EALREADY);
        }
#endif
#ifdef INET6
        if (V_udp6_tun_socket != NULL) {
                /* Already running -- must stop first */
                return (EALREADY);
        }
#endif
#ifdef INET
        if ((ret = socreate(PF_INET, &V_udp4_tun_socket,
            SOCK_DGRAM, IPPROTO_UDP,
            curthread->td_ucred, curthread))) {
                tcp_over_udp_stop();
                return (ret);
        }
        /* Call the special UDP hook. */
        if ((ret = udp_set_kernel_tunneling(V_udp4_tun_socket,
            tcp_recv_udp_tunneled_packet,
            tcp_ctlinput_viaudp,
            NULL))) {
                tcp_over_udp_stop();
                return (ret);
        }
        /* Ok, we have a socket, bind it to the port. */
        memset(&sin, 0, sizeof(struct sockaddr_in));
        sin.sin_len = sizeof(struct sockaddr_in);
        sin.sin_family = AF_INET;
        sin.sin_port = htons(port);
        if ((ret = sobind(V_udp4_tun_socket,
            (struct sockaddr *)&sin, curthread))) {
                tcp_over_udp_stop();
                return (ret);
        }
#endif
#ifdef INET6
        if ((ret = socreate(PF_INET6, &V_udp6_tun_socket,
            SOCK_DGRAM, IPPROTO_UDP,
            curthread->td_ucred, curthread))) {
                tcp_over_udp_stop();
                return (ret);
        }
        /* Call the special UDP hook. */
        if ((ret = udp_set_kernel_tunneling(V_udp6_tun_socket,
            tcp_recv_udp_tunneled_packet,
            tcp6_ctlinput_viaudp,
            NULL))) {
                tcp_over_udp_stop();
                return (ret);
        }
        /* Ok, we have a socket, bind it to the port. */
        memset(&sin6, 0, sizeof(struct sockaddr_in6));
        sin6.sin6_len = sizeof(struct sockaddr_in6);
        sin6.sin6_family = AF_INET6;
        sin6.sin6_port = htons(port);
        if ((ret = sobind(V_udp6_tun_socket,
            (struct sockaddr *)&sin6, curthread))) {
                tcp_over_udp_stop();
                return (ret);
        }
#endif
        return (0);
}

static int
sysctl_net_inet_tcp_udp_tunneling_port_check(SYSCTL_HANDLER_ARGS)
{
        int error;
        uint32_t old, new;

        old = V_tcp_udp_tunneling_port;
        new = old;
        error = sysctl_handle_int(oidp, &new, 0, req);
        if ((error == 0) &&
            (req->newptr != NULL)) {
                if ((new < TCP_TUNNELING_PORT_MIN) ||
                    (new > TCP_TUNNELING_PORT_MAX)) {
                        error = EINVAL;
                } else {
                        sx_xlock(&tcpoudp_lock);
                        V_tcp_udp_tunneling_port = new;
                        if (old != 0) {
                                tcp_over_udp_stop();
                        }
                        if (new != 0) {
                                error = tcp_over_udp_start();
                                if (error != 0) {
                                        V_tcp_udp_tunneling_port = 0;
                                }
                        }
                        sx_xunlock(&tcpoudp_lock);
                }
        }
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, udp_tunneling_port,
    CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE,
    &VNET_NAME(tcp_udp_tunneling_port),
    0, &sysctl_net_inet_tcp_udp_tunneling_port_check, "IU",
    "Tunneling port for tcp over udp");

VNET_DEFINE(int, tcp_udp_tunneling_overhead) = TCP_TUNNELING_OVERHEAD_DEFAULT;

static int
sysctl_net_inet_tcp_udp_tunneling_overhead_check(SYSCTL_HANDLER_ARGS)
{
        int error, new;

        new = V_tcp_udp_tunneling_overhead;
        error = sysctl_handle_int(oidp, &new, 0, req);
        if (error == 0 && req->newptr) {
                if ((new < TCP_TUNNELING_OVERHEAD_MIN) ||
                    (new > TCP_TUNNELING_OVERHEAD_MAX))
                        error = EINVAL;
                else
                        V_tcp_udp_tunneling_overhead = new;
        }
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, udp_tunneling_overhead,
    CTLFLAG_VNET | CTLTYPE_INT | CTLFLAG_RW | CTLFLAG_MPSAFE,
    &VNET_NAME(tcp_udp_tunneling_overhead),
    0, &sysctl_net_inet_tcp_udp_tunneling_overhead_check, "IU",
    "MSS reduction when using tcp over udp");

/*
 * Exports one (struct tcp_function_info) for each alias/name.
 */
static int
sysctl_net_inet_list_func_info(SYSCTL_HANDLER_ARGS)
{
        int cnt, error;
        struct tcp_function *f;
        struct tcp_function_info tfi;

        /*
         * We don't allow writes.
         */
        if (req->newptr != NULL)
                return (EINVAL);

        /*
         * Wire the old buffer so we can directly copy the functions to
         * user space without dropping the lock.
         */
        if (req->oldptr != NULL) {
                error = sysctl_wire_old_buffer(req, 0);
                if (error)
                        return (error);
        }

        /*
         * Walk the list and copy out matching entries. If INVARIANTS
         * is compiled in, also walk the list to verify the length of
         * the list matches what we have recorded.
         */
        rw_rlock(&tcp_function_lock);

        cnt = 0;
#ifndef INVARIANTS
        if (req->oldptr == NULL) {
                cnt = tcp_fb_cnt;
                goto skip_loop;
        }
#endif
        TAILQ_FOREACH(f, &t_functions, tf_next) {
#ifdef INVARIANTS
                cnt++;
#endif
                if (req->oldptr != NULL) {
                        bzero(&tfi, sizeof(tfi));
                        tfi.tfi_refcnt = f->tf_fb->tfb_refcnt;
                        tfi.tfi_id = f->tf_fb->tfb_id;
                        (void)strlcpy(tfi.tfi_alias, f->tf_name,
                            sizeof(tfi.tfi_alias));
                        (void)strlcpy(tfi.tfi_name,
                            f->tf_fb->tfb_tcp_block_name, sizeof(tfi.tfi_name));
                        error = SYSCTL_OUT(req, &tfi, sizeof(tfi));
                        /*
                         * Don't stop on error, as that is the
                         * mechanism we use to accumulate length
                         * information if the buffer was too short.
                         */
                }
        }
        KASSERT(cnt == tcp_fb_cnt,
            ("%s: cnt (%d) != tcp_fb_cnt (%d)", __func__, cnt, tcp_fb_cnt));
#ifndef INVARIANTS
skip_loop:
#endif
        rw_runlock(&tcp_function_lock);
        if (req->oldptr == NULL)
                error = SYSCTL_OUT(req, NULL,
                    (cnt + 1) * sizeof(struct tcp_function_info));

        return (error);
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, function_info,
            CTLTYPE_OPAQUE | CTLFLAG_SKIP | CTLFLAG_RD | CTLFLAG_MPSAFE,
            NULL, 0, sysctl_net_inet_list_func_info, "S,tcp_function_info",
            "List TCP function block name-to-ID mappings");

/*
 * tfb_tcp_handoff_ok() function for the default stack.
 * Note that we'll basically try to take all comers.
 */
static int
tcp_default_handoff_ok(struct tcpcb *tp)
{

        return (0);
}

/*
 * tfb_tcp_fb_init() function for the default stack.
 *
 * This handles making sure we have appropriate timers set if you are
 * transitioning a socket that has some amount of setup done.
 *
 * The init() fuction from the default can *never* return non-zero i.e.
 * it is required to always succeed since it is the stack of last resort!
 */
static int
tcp_default_fb_init(struct tcpcb *tp)
{
        struct socket *so = tptosocket(tp);

        INP_WLOCK_ASSERT(tptoinpcb(tp));

        KASSERT(tp->t_state >= 0 && tp->t_state < TCPS_TIME_WAIT,
            ("%s: connection %p in unexpected state %d", __func__, tp,
            tp->t_state));

        /*
         * Nothing to do for ESTABLISHED or LISTEN states. And, we don't
         * know what to do for unexpected states (which includes TIME_WAIT).
         */
        if (tp->t_state <= TCPS_LISTEN || tp->t_state >= TCPS_TIME_WAIT)
                return (0);

        /*
         * Make sure some kind of transmission timer is set if there is
         * outstanding data.
         */
        if ((!TCPS_HAVEESTABLISHED(tp->t_state) || sbavail(&so->so_snd) ||
            tp->snd_una != tp->snd_max) && !(tcp_timer_active(tp, TT_REXMT) ||
            tcp_timer_active(tp, TT_PERSIST))) {
                /*
                 * If the session has established and it looks like it should
                 * be in the persist state, set the persist timer. Otherwise,
                 * set the retransmit timer.
                 */
                if (TCPS_HAVEESTABLISHED(tp->t_state) && tp->snd_wnd == 0 &&
                    (int32_t)(tp->snd_nxt - tp->snd_una) <
                    (int32_t)sbavail(&so->so_snd))
                        tcp_setpersist(tp);
                else
                        tcp_timer_activate(tp, TT_REXMT, tp->t_rxtcur);
        }

        /* All non-embryonic sessions get a keepalive timer. */
        if (!tcp_timer_active(tp, TT_KEEP))
                tcp_timer_activate(tp, TT_KEEP,
                    TCPS_HAVEESTABLISHED(tp->t_state) ? TP_KEEPIDLE(tp) :
                    TP_KEEPINIT(tp));

        /*
         * Make sure critical variables are initialized
         * if transitioning while in Recovery.
         */
        if IN_FASTRECOVERY(tp->t_flags) {
                if (tp->sackhint.recover_fs == 0)
                        tp->sackhint.recover_fs = max(1,
                            tp->snd_nxt - tp->snd_una);
        }

        return (0);
}

/*
 * tfb_tcp_fb_fini() function for the default stack.
 *
 * This changes state as necessary (or prudent) to prepare for another stack
 * to assume responsibility for the connection.
 */
static void
tcp_default_fb_fini(struct tcpcb *tp, int tcb_is_purged)
{

        INP_WLOCK_ASSERT(tptoinpcb(tp));
}

/*
 * Target size of TCP PCB hash tables. Must be a power of two.
 *
 * Note that this can be overridden by the kernel environment
 * variable net.inet.tcp.tcbhashsize
 */
#ifndef TCBHASHSIZE
#define TCBHASHSIZE     0
#endif

MALLOC_DEFINE(M_TCPLOG, "tcplog", "TCP address and flags print buffers");
MALLOC_DEFINE(M_TCPFUNCTIONS, "tcpfunc", "TCP function set memory");

static struct mtx isn_mtx;

#define ISN_LOCK_INIT() mtx_init(&isn_mtx, "isn_mtx", NULL, MTX_DEF)
#define ISN_LOCK()      mtx_lock(&isn_mtx)
#define ISN_UNLOCK()    mtx_unlock(&isn_mtx)

INPCBSTORAGE_DEFINE(tcpcbstor, tcpcb, "tcpinp", "tcp_inpcb", "tcp", "tcphash");

/*
 * Take a value and get the next power of 2 that doesn't overflow.
 * Used to size the tcp_inpcb hash buckets.
 */
static int
maketcp_hashsize(int size)
{
        int hashsize;

        /*
         * auto tune.
         * get the next power of 2 higher than maxsockets.
         */
        hashsize = 1 << fls(size);
        /* catch overflow, and just go one power of 2 smaller */
        if (hashsize < size) {
                hashsize = 1 << (fls(size) - 1);
        }
        return (hashsize);
}

static volatile int next_tcp_stack_id = 1;

/*
 * Register a TCP function block with the name provided in the names
 * array.  (Note that this function does NOT automatically register
 * blk->tfb_tcp_block_name as a stack name.  Therefore, you should
 * explicitly include blk->tfb_tcp_block_name in the list of names if
 * you wish to register the stack with that name.)
 *
 * Either all name registrations will succeed or all will fail.  If
 * a name registration fails, the function will update the num_names
 * argument to point to the array index of the name that encountered
 * the failure.
 *
 * Returns 0 on success, or an error code on failure.
 */
int
register_tcp_functions_as_names(struct tcp_function_block *blk, int wait,
    const char *names[], int *num_names)
{
        struct tcp_function *n;
        struct tcp_function_set fs;
        int error, i;

        KASSERT(names != NULL && *num_names > 0,
            ("%s: Called with 0-length name list", __func__));
        KASSERT(names != NULL, ("%s: Called with NULL name list", __func__));
        KASSERT(rw_initialized(&tcp_function_lock),
            ("%s: called too early", __func__));

        if ((blk->tfb_tcp_output == NULL) ||
            (blk->tfb_tcp_do_segment == NULL) ||
            (blk->tfb_tcp_ctloutput == NULL) ||
            (strlen(blk->tfb_tcp_block_name) == 0)) {
                /*
                 * These functions are required and you
                 * need a name.
                 */
                *num_names = 0;
                return (EINVAL);
        }

        if (blk->tfb_flags & TCP_FUNC_BEING_REMOVED) {
                *num_names = 0;
                return (EINVAL);
        }

        refcount_init(&blk->tfb_refcnt, 0);
        blk->tfb_id = atomic_fetchadd_int(&next_tcp_stack_id, 1);
        for (i = 0; i < *num_names; i++) {
                n = malloc(sizeof(struct tcp_function), M_TCPFUNCTIONS, wait);
                if (n == NULL) {
                        error = ENOMEM;
                        goto cleanup;
                }
                n->tf_fb = blk;

                (void)strlcpy(fs.function_set_name, names[i],
                    sizeof(fs.function_set_name));
                rw_wlock(&tcp_function_lock);
                if (find_tcp_functions_locked(&fs) != NULL) {
                        /* Duplicate name space not allowed */
                        rw_wunlock(&tcp_function_lock);
                        free(n, M_TCPFUNCTIONS);
                        error = EALREADY;
                        goto cleanup;
                }
                (void)strlcpy(n->tf_name, names[i], sizeof(n->tf_name));
                TAILQ_INSERT_TAIL(&t_functions, n, tf_next);
                tcp_fb_cnt++;
                rw_wunlock(&tcp_function_lock);
        }
        return(0);

cleanup:
        /*
         * Deregister the names we just added. Because registration failed
         * for names[i], we don't need to deregister that name.
         */
        *num_names = i;
        rw_wlock(&tcp_function_lock);
        while (--i >= 0) {
                TAILQ_FOREACH(n, &t_functions, tf_next) {
                        if (!strncmp(n->tf_name, names[i],
                            TCP_FUNCTION_NAME_LEN_MAX)) {
                                TAILQ_REMOVE(&t_functions, n, tf_next);
                                tcp_fb_cnt--;
                                n->tf_fb = NULL;
                                free(n, M_TCPFUNCTIONS);
                                break;
                        }
                }
        }
        rw_wunlock(&tcp_function_lock);
        return (error);
}

/*
 * Register a TCP function block using the name provided in the name
 * argument.
 *
 * Returns 0 on success, or an error code on failure.
 */
int
register_tcp_functions_as_name(struct tcp_function_block *blk, const char *name,
    int wait)
{
        const char *name_list[1];
        int num_names, rv;

        num_names = 1;
        if (name != NULL)
                name_list[0] = name;
        else
                name_list[0] = blk->tfb_tcp_block_name;
        rv = register_tcp_functions_as_names(blk, wait, name_list, &num_names);
        return (rv);
}

/*
 * Register a TCP function block using the name defined in
 * blk->tfb_tcp_block_name.
 *
 * Returns 0 on success, or an error code on failure.
 */
int
register_tcp_functions(struct tcp_function_block *blk, int wait)
{

        return (register_tcp_functions_as_name(blk, NULL, wait));
}

/*
 * Deregister all names associated with a function block. This
 * functionally removes the function block from use within the system.
 *
 * When called with a true quiesce argument, mark the function block
 * as being removed so no more stacks will use it and determine
 * whether the removal would succeed.
 *
 * When called with a false quiesce argument, actually attempt the
 * removal.
 *
 * When called with a force argument, attempt to switch all TCBs to
 * use the default stack instead of returning EBUSY.
 *
 * Returns 0 on success (or if the removal would succeed, or an error
 * code on failure.
 */
int
deregister_tcp_functions(struct tcp_function_block *blk, bool quiesce,
    bool force)
{
        struct tcp_function *f;

        if (blk == &tcp_def_funcblk) {
                /* You can't un-register the default */
                return (EPERM);
        }
        rw_wlock(&tcp_function_lock);
        if (blk == tcp_func_set_ptr) {
                /* You can't free the current default */
                rw_wunlock(&tcp_function_lock);
                return (EBUSY);
        }
        /* Mark the block so no more stacks can use it. */
        blk->tfb_flags |= TCP_FUNC_BEING_REMOVED;
        /*
         * If TCBs are still attached to the stack, attempt to switch them
         * to the default stack.
         */
        if (force && blk->tfb_refcnt) {
                struct inpcb_iterator inpi = INP_ALL_ITERATOR(&V_tcbinfo,
                    INPLOOKUP_WLOCKPCB);
                struct inpcb *inp;
                struct tcpcb *tp;
                VNET_ITERATOR_DECL(vnet_iter);

                rw_wunlock(&tcp_function_lock);

                VNET_LIST_RLOCK();
                VNET_FOREACH(vnet_iter) {
                        CURVNET_SET(vnet_iter);
                        while ((inp = inp_next(&inpi)) != NULL) {
                                tp = intotcpcb(inp);
                                if (tp == NULL || tp->t_fb != blk)
                                        continue;
                                tcp_switch_back_to_default(tp);
                        }
                        CURVNET_RESTORE();
                }
                VNET_LIST_RUNLOCK();

                rw_wlock(&tcp_function_lock);
        }
        if (blk->tfb_refcnt) {
                /* TCBs still attached. */
                rw_wunlock(&tcp_function_lock);
                return (EBUSY);
        }
        if (quiesce) {
                /* Skip removal. */
                rw_wunlock(&tcp_function_lock);
                return (0);
        }
        /* Remove any function names that map to this function block. */
        while (find_tcp_fb_locked(blk, &f) != NULL) {
                TAILQ_REMOVE(&t_functions, f, tf_next);
                tcp_fb_cnt--;
                f->tf_fb = NULL;
                free(f, M_TCPFUNCTIONS);
        }
        rw_wunlock(&tcp_function_lock);
        return (0);
}

static void
tcp_drain(void)
{
        struct epoch_tracker et;
        VNET_ITERATOR_DECL(vnet_iter);

        if (!do_tcpdrain)
                return;

        NET_EPOCH_ENTER(et);
        VNET_LIST_RLOCK_NOSLEEP();
        VNET_FOREACH(vnet_iter) {
                CURVNET_SET(vnet_iter);
                struct inpcb_iterator inpi = INP_ALL_ITERATOR(&V_tcbinfo,
                    INPLOOKUP_WLOCKPCB);
                struct inpcb *inpb;
                struct tcpcb *tcpb;

        /*
         * Walk the tcpbs, if existing, and flush the reassembly queue,
         * if there is one...
         * XXX: The "Net/3" implementation doesn't imply that the TCP
         *      reassembly queue should be flushed, but in a situation
         *      where we're really low on mbufs, this is potentially
         *      useful.
         */
                while ((inpb = inp_next(&inpi)) != NULL) {
                        if ((tcpb = intotcpcb(inpb)) != NULL) {
                                tcp_reass_flush(tcpb);
                                tcp_clean_sackreport(tcpb);
#ifdef TCP_BLACKBOX
                                tcp_log_drain(tcpb);
#endif
#ifdef TCPPCAP
                                if (tcp_pcap_aggressive_free) {
                                        /* Free the TCP PCAP queues. */
                                        tcp_pcap_drain(&(tcpb->t_inpkts));
                                        tcp_pcap_drain(&(tcpb->t_outpkts));
                                }
#endif
                        }
                }
                CURVNET_RESTORE();
        }
        VNET_LIST_RUNLOCK_NOSLEEP();
        NET_EPOCH_EXIT(et);
}

static void
tcp_vnet_init(void *arg __unused)
{

#ifdef TCP_HHOOK
        if (hhook_head_register(HHOOK_TYPE_TCP, HHOOK_TCP_EST_IN,
            &V_tcp_hhh[HHOOK_TCP_EST_IN], HHOOK_NOWAIT|HHOOK_HEADISINVNET) != 0)
                printf("%s: WARNING: unable to register helper hook\n", __func__);
        if (hhook_head_register(HHOOK_TYPE_TCP, HHOOK_TCP_EST_OUT,
            &V_tcp_hhh[HHOOK_TCP_EST_OUT], HHOOK_NOWAIT|HHOOK_HEADISINVNET) != 0)
                printf("%s: WARNING: unable to register helper hook\n", __func__);
#endif
#ifdef STATS
        if (tcp_stats_init())
                printf("%s: WARNING: unable to initialise TCP stats\n",
                    __func__);
#endif
        in_pcbinfo_init(&V_tcbinfo, &tcpcbstor, tcp_tcbhashsize,
            tcp_tcbhashsize);

        syncache_init();
        tcp_hc_init();

        TUNABLE_INT_FETCH("net.inet.tcp.sack.enable", &V_tcp_do_sack);
        V_sack_hole_zone = uma_zcreate("sackhole", sizeof(struct sackhole),
            NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);

        tcp_fastopen_init();

        COUNTER_ARRAY_ALLOC(V_tcps_states, TCP_NSTATES, M_WAITOK);
        VNET_PCPUSTAT_ALLOC(tcpstat, M_WAITOK);

        V_tcp_msl = TCPTV_MSL;
}
VNET_SYSINIT(tcp_vnet_init, SI_SUB_PROTO_DOMAIN, SI_ORDER_FOURTH,
    tcp_vnet_init, NULL);

static void
tcp_init(void *arg __unused)
{
        const char *tcbhash_tuneable;
        int hashsize;

        tcp_reass_global_init();

        /* XXX virtualize those below? */
        tcp_delacktime = TCPTV_DELACK;
        tcp_keepinit = TCPTV_KEEP_INIT;
        tcp_keepidle = TCPTV_KEEP_IDLE;
        tcp_keepintvl = TCPTV_KEEPINTVL;
        tcp_maxpersistidle = TCPTV_KEEP_IDLE;
        tcp_rexmit_initial = TCPTV_RTOBASE;
        if (tcp_rexmit_initial < 1)
                tcp_rexmit_initial = 1;
        tcp_rexmit_min = TCPTV_MIN;
        if (tcp_rexmit_min < 1)
                tcp_rexmit_min = 1;
        tcp_persmin = TCPTV_PERSMIN;
        tcp_persmax = TCPTV_PERSMAX;
        tcp_rexmit_slop = TCPTV_CPU_VAR;
        tcp_finwait2_timeout = TCPTV_FINWAIT2_TIMEOUT;

        /* Setup the tcp function block list */
        TAILQ_INIT(&t_functions);
        rw_init(&tcp_function_lock, "tcp_func_lock");
        register_tcp_functions(&tcp_def_funcblk, M_WAITOK);
        sx_init(&tcpoudp_lock, "TCP over UDP configuration");
#ifdef TCP_BLACKBOX
        /* Initialize the TCP logging data. */
        tcp_log_init();
#endif
        arc4rand(&V_ts_offset_secret, sizeof(V_ts_offset_secret), 0);

        if (tcp_soreceive_stream) {
#ifdef INET
                tcp_protosw.pr_soreceive = soreceive_stream;
#endif
#ifdef INET6
                tcp6_protosw.pr_soreceive = soreceive_stream;
#endif /* INET6 */
        }

#ifdef INET6
        max_protohdr_grow(sizeof(struct ip6_hdr) + sizeof(struct tcphdr));
#else /* INET6 */
        max_protohdr_grow(sizeof(struct tcpiphdr));
#endif /* INET6 */

        ISN_LOCK_INIT();
        EVENTHANDLER_REGISTER(shutdown_pre_sync, tcp_fini, NULL,
                SHUTDOWN_PRI_DEFAULT);
        EVENTHANDLER_REGISTER(vm_lowmem, tcp_drain, NULL, LOWMEM_PRI_DEFAULT);
        EVENTHANDLER_REGISTER(mbuf_lowmem, tcp_drain, NULL, LOWMEM_PRI_DEFAULT);

        tcp_inp_lro_direct_queue = counter_u64_alloc(M_WAITOK);
        tcp_inp_lro_wokeup_queue = counter_u64_alloc(M_WAITOK);
        tcp_inp_lro_compressed = counter_u64_alloc(M_WAITOK);
        tcp_inp_lro_locks_taken = counter_u64_alloc(M_WAITOK);
        tcp_extra_mbuf = counter_u64_alloc(M_WAITOK);
        tcp_would_have_but = counter_u64_alloc(M_WAITOK);
        tcp_comp_total = counter_u64_alloc(M_WAITOK);
        tcp_uncomp_total = counter_u64_alloc(M_WAITOK);
        tcp_bad_csums = counter_u64_alloc(M_WAITOK);
#ifdef TCPPCAP
        tcp_pcap_init();
#endif

        hashsize = TCBHASHSIZE;
        tcbhash_tuneable = "net.inet.tcp.tcbhashsize";
        TUNABLE_INT_FETCH(tcbhash_tuneable, &hashsize);
        if (hashsize == 0) {
                /*
                 * Auto tune the hash size based on maxsockets.
                 * A perfect hash would have a 1:1 mapping
                 * (hashsize = maxsockets) however it's been
                 * suggested that O(2) average is better.
                 */
                hashsize = maketcp_hashsize(maxsockets / 4);
                /*
                 * Our historical default is 512,
                 * do not autotune lower than this.
                 */
                if (hashsize < 512)
                        hashsize = 512;
                if (bootverbose)
                        printf("%s: %s auto tuned to %d\n", __func__,
                            tcbhash_tuneable, hashsize);
        }
        /*
         * We require a hashsize to be a power of two.
         * Previously if it was not a power of two we would just reset it
         * back to 512, which could be a nasty surprise if you did not notice
         * the error message.
         * Instead what we do is clip it to the closest power of two lower
         * than the specified hash value.
         */
        if (!powerof2(hashsize)) {
                int oldhashsize = hashsize;

                hashsize = maketcp_hashsize(hashsize);
                /* prevent absurdly low value */
                if (hashsize < 16)
                        hashsize = 16;
                printf("%s: WARNING: TCB hash size not a power of 2, "
                    "clipped from %d to %d.\n", __func__, oldhashsize,
                    hashsize);
        }
        tcp_tcbhashsize = hashsize;

#ifdef INET
        IPPROTO_REGISTER(IPPROTO_TCP, tcp_input, tcp_ctlinput);
#endif
#ifdef INET6
        IP6PROTO_REGISTER(IPPROTO_TCP, tcp6_input, tcp6_ctlinput);
#endif
}
SYSINIT(tcp_init, SI_SUB_PROTO_DOMAIN, SI_ORDER_THIRD, tcp_init, NULL);

#ifdef VIMAGE
static void
tcp_destroy(void *unused __unused)
{
        int n;
#ifdef TCP_HHOOK
        int error;
#endif

        /*
         * All our processes are gone, all our sockets should be cleaned
         * up, which means, we should be past the tcp_discardcb() calls.
         * Sleep to let all tcpcb timers really disappear and cleanup.
         */
        for (;;) {
                INP_INFO_WLOCK(&V_tcbinfo);
                n = V_tcbinfo.ipi_count;
                INP_INFO_WUNLOCK(&V_tcbinfo);
                if (n == 0)
                        break;
                pause("tcpdes", hz / 10);
        }
        tcp_hc_destroy();
        syncache_destroy();
        in_pcbinfo_destroy(&V_tcbinfo);
        /* tcp_discardcb() clears the sack_holes up. */
        uma_zdestroy(V_sack_hole_zone);

        /*
         * Cannot free the zone until all tcpcbs are released as we attach
         * the allocations to them.
         */
        tcp_fastopen_destroy();

        COUNTER_ARRAY_FREE(V_tcps_states, TCP_NSTATES);
        VNET_PCPUSTAT_FREE(tcpstat);

#ifdef TCP_HHOOK
        error = hhook_head_deregister(V_tcp_hhh[HHOOK_TCP_EST_IN]);
        if (error != 0) {
                printf("%s: WARNING: unable to deregister helper hook "
                    "type=%d, id=%d: error %d returned\n", __func__,
                    HHOOK_TYPE_TCP, HHOOK_TCP_EST_IN, error);
        }
        error = hhook_head_deregister(V_tcp_hhh[HHOOK_TCP_EST_OUT]);
        if (error != 0) {
                printf("%s: WARNING: unable to deregister helper hook "
                    "type=%d, id=%d: error %d returned\n", __func__,
                    HHOOK_TYPE_TCP, HHOOK_TCP_EST_OUT, error);
        }
#endif
}
VNET_SYSUNINIT(tcp, SI_SUB_PROTO_DOMAIN, SI_ORDER_FOURTH, tcp_destroy, NULL);
#endif

void
tcp_fini(void *xtp)
{

}

/*
 * Fill in the IP and TCP headers for an outgoing packet, given the tcpcb.
 * tcp_template used to store this data in mbufs, but we now recopy it out
 * of the tcpcb each time to conserve mbufs.
 */
void
tcpip_fillheaders(struct inpcb *inp, uint16_t port, void *ip_ptr, void *tcp_ptr)
{
        struct tcphdr *th = (struct tcphdr *)tcp_ptr;

        INP_WLOCK_ASSERT(inp);

#ifdef INET6
        if ((inp->inp_vflag & INP_IPV6) != 0) {
                struct ip6_hdr *ip6;

                ip6 = (struct ip6_hdr *)ip_ptr;
                ip6->ip6_flow = (ip6->ip6_flow & ~IPV6_FLOWINFO_MASK) |
                        (inp->inp_flow & IPV6_FLOWINFO_MASK);
                ip6->ip6_vfc = (ip6->ip6_vfc & ~IPV6_VERSION_MASK) |
                        (IPV6_VERSION & IPV6_VERSION_MASK);
                if (port == 0)
                        ip6->ip6_nxt = IPPROTO_TCP;
                else
                        ip6->ip6_nxt = IPPROTO_UDP;
                ip6->ip6_plen = htons(sizeof(struct tcphdr));
                ip6->ip6_src = inp->in6p_laddr;
                ip6->ip6_dst = inp->in6p_faddr;
        }
#endif /* INET6 */
#if defined(INET6) && defined(INET)
        else
#endif
#ifdef INET
        {
                struct ip *ip;

                ip = (struct ip *)ip_ptr;
                ip->ip_v = IPVERSION;
                ip->ip_hl = 5;
                ip->ip_tos = inp->inp_ip_tos;
                ip->ip_len = 0;
                ip->ip_id = 0;
                ip->ip_off = 0;
                ip->ip_ttl = inp->inp_ip_ttl;
                ip->ip_sum = 0;
                if (port == 0)
                        ip->ip_p = IPPROTO_TCP;
                else
                        ip->ip_p = IPPROTO_UDP;
                ip->ip_src = inp->inp_laddr;
                ip->ip_dst = inp->inp_faddr;
        }
#endif /* INET */
        th->th_sport = inp->inp_lport;
        th->th_dport = inp->inp_fport;
        th->th_seq = 0;
        th->th_ack = 0;
        th->th_off = 5;
        tcp_set_flags(th, 0);
        th->th_win = 0;
        th->th_urp = 0;
        th->th_sum = 0;         /* in_pseudo() is called later for ipv4 */
}

/*
 * Create template to be used to send tcp packets on a connection.
 * Allocates an mbuf and fills in a skeletal tcp/ip header.  The only
 * use for this function is in keepalives, which use tcp_respond.
 */
struct tcptemp *
tcpip_maketemplate(struct inpcb *inp)
{
        struct tcptemp *t;

        t = malloc(sizeof(*t), M_TEMP, M_NOWAIT);
        if (t == NULL)
                return (NULL);
        tcpip_fillheaders(inp, 0, (void *)&t->tt_ipgen, (void *)&t->tt_t);
        return (t);
}

/*
 * Send a single message to the TCP at address specified by
 * the given TCP/IP header.  If m == NULL, then we make a copy
 * of the tcpiphdr at th and send directly to the addressed host.
 * This is used to force keep alive messages out using the TCP
 * template for a connection.  If flags are given then we send
 * a message back to the TCP which originated the segment th,
 * and discard the mbuf containing it and any other attached mbufs.
 *
 * In any case the ack and sequence number of the transmitted
 * segment are as specified by the parameters.
 *
 * NOTE: If m != NULL, then th must point to *inside* the mbuf.
 */
void
tcp_respond(struct tcpcb *tp, void *ipgen, struct tcphdr *th, struct mbuf *m,
    tcp_seq ack, tcp_seq seq, uint16_t flags)
{
        struct tcpopt to;
        struct inpcb *inp;
        struct ip *ip;
        struct mbuf *optm;
        struct udphdr *uh = NULL;
        struct tcphdr *nth;
        struct tcp_log_buffer *lgb;
        u_char *optp;
#ifdef INET6
        struct ip6_hdr *ip6;
        int isipv6;
#endif /* INET6 */
        int optlen, tlen, win, ulen;
        int ect = 0;
        bool incl_opts;
        uint16_t port;
        int output_ret;
#ifdef INVARIANTS
        int thflags = tcp_get_flags(th);
#endif

        KASSERT(tp != NULL || m != NULL, ("tcp_respond: tp and m both NULL"));
        NET_EPOCH_ASSERT();

#ifdef INET6
        isipv6 = ((struct ip *)ipgen)->ip_v == (IPV6_VERSION >> 4);
        ip6 = ipgen;
#endif /* INET6 */
        ip = ipgen;

        if (tp != NULL) {
                inp = tptoinpcb(tp);
                INP_LOCK_ASSERT(inp);
        } else
                inp = NULL;

        if (m != NULL) {
#ifdef INET6
                if (isipv6 && ip6 && (ip6->ip6_nxt == IPPROTO_UDP))
                        port = m->m_pkthdr.tcp_tun_port;
                else
#endif
                if (ip && (ip->ip_p == IPPROTO_UDP))
                        port = m->m_pkthdr.tcp_tun_port;
                else
                        port = 0;
        } else
                port = tp->t_port;

        incl_opts = false;
        win = 0;
        if (tp != NULL) {
                if (!(flags & TH_RST)) {
                        win = sbspace(&inp->inp_socket->so_rcv);
                        if (win > TCP_MAXWIN << tp->rcv_scale)
                                win = TCP_MAXWIN << tp->rcv_scale;
                }
                if ((tp->t_flags & TF_NOOPT) == 0)
                        incl_opts = true;
        }
        if (m == NULL) {
                m = m_gethdr(M_NOWAIT, MT_DATA);
                if (m == NULL)
                        return;
                m->m_data += max_linkhdr;
#ifdef INET6
                if (isipv6) {
                        bcopy((caddr_t)ip6, mtod(m, caddr_t),
                              sizeof(struct ip6_hdr));
                        ip6 = mtod(m, struct ip6_hdr *);
                        nth = (struct tcphdr *)(ip6 + 1);
                        if (port) {
                                /* Insert a UDP header */
                                uh = (struct udphdr *)nth;
                                uh->uh_sport = htons(V_tcp_udp_tunneling_port);
                                uh->uh_dport = port;
                                nth = (struct tcphdr *)(uh + 1);
                        }
                } else
#endif /* INET6 */
                {
                        bcopy((caddr_t)ip, mtod(m, caddr_t), sizeof(struct ip));
                        ip = mtod(m, struct ip *);
                        nth = (struct tcphdr *)(ip + 1);
                        if (port) {
                                /* Insert a UDP header */
                                uh = (struct udphdr *)nth;
                                uh->uh_sport = htons(V_tcp_udp_tunneling_port);
                                uh->uh_dport = port;
                                nth = (struct tcphdr *)(uh + 1);
                        }
                }
                bcopy((caddr_t)th, (caddr_t)nth, sizeof(struct tcphdr));
                flags = TH_ACK;
        } else if ((!M_WRITABLE(m)) || (port != 0)) {
                struct mbuf *n;

                /* Can't reuse 'm', allocate a new mbuf. */
                n = m_gethdr(M_NOWAIT, MT_DATA);
                if (n == NULL) {
                        m_freem(m);
                        return;
                }

                if (!m_dup_pkthdr(n, m, M_NOWAIT)) {
                        m_freem(m);
                        m_freem(n);
                        return;
                }

                n->m_data += max_linkhdr;
                /* m_len is set later */
#define xchg(a,b,type) { type t; t=a; a=b; b=t; }
#ifdef INET6
                if (isipv6) {
                        bcopy((caddr_t)ip6, mtod(n, caddr_t),
                              sizeof(struct ip6_hdr));
                        ip6 = mtod(n, struct ip6_hdr *);
                        xchg(ip6->ip6_dst, ip6->ip6_src, struct in6_addr);
                        nth = (struct tcphdr *)(ip6 + 1);
                        if (port) {
                                /* Insert a UDP header */
                                uh = (struct udphdr *)nth;
                                uh->uh_sport = htons(V_tcp_udp_tunneling_port);
                                uh->uh_dport = port;
                                nth = (struct tcphdr *)(uh + 1);
                        }
                } else
#endif /* INET6 */
                {
                        bcopy((caddr_t)ip, mtod(n, caddr_t), sizeof(struct ip));
                        ip = mtod(n, struct ip *);
                        xchg(ip->ip_dst.s_addr, ip->ip_src.s_addr, uint32_t);
                        nth = (struct tcphdr *)(ip + 1);
                        if (port) {
                                /* Insert a UDP header */
                                uh = (struct udphdr *)nth;
                                uh->uh_sport = htons(V_tcp_udp_tunneling_port);
                                uh->uh_dport = port;
                                nth = (struct tcphdr *)(uh + 1);
                        }
                }
                bcopy((caddr_t)th, (caddr_t)nth, sizeof(struct tcphdr));
                xchg(nth->th_dport, nth->th_sport, uint16_t);
                th = nth;
                m_freem(m);
                m = n;
        } else {
                /*
                 *  reuse the mbuf.
                 * XXX MRT We inherit the FIB, which is lucky.
                 */
                m_freem(m->m_next);
                m->m_next = NULL;
                m->m_data = (caddr_t)ipgen;
                /* m_len is set later */
#ifdef INET6
                if (isipv6) {
                        xchg(ip6->ip6_dst, ip6->ip6_src, struct in6_addr);
                        nth = (struct tcphdr *)(ip6 + 1);
                } else
#endif /* INET6 */
                {
                        xchg(ip->ip_dst.s_addr, ip->ip_src.s_addr, uint32_t);
                        nth = (struct tcphdr *)(ip + 1);
                }
                if (th != nth) {
                        /*
                         * this is usually a case when an extension header
                         * exists between the IPv6 header and the
                         * TCP header.
                         */
                        nth->th_sport = th->th_sport;
                        nth->th_dport = th->th_dport;
                }
                xchg(nth->th_dport, nth->th_sport, uint16_t);
#undef xchg
        }
        tlen = 0;
#ifdef INET6
        if (isipv6)
                tlen = sizeof (struct ip6_hdr) + sizeof (struct tcphdr);
#endif
#if defined(INET) && defined(INET6)
        else
#endif
#ifdef INET
                tlen = sizeof (struct tcpiphdr);
#endif
        if (port)
                tlen += sizeof (struct udphdr);
#ifdef INVARIANTS
        m->m_len = 0;
        KASSERT(M_TRAILINGSPACE(m) >= tlen,
            ("Not enough trailing space for message (m=%p, need=%d, have=%ld)",
            m, tlen, (long)M_TRAILINGSPACE(m)));
#endif
        m->m_len = tlen;
        to.to_flags = 0;
        if (incl_opts) {
                ect = tcp_ecn_output_established(tp, &flags, 0, false);
                /* Make sure we have room. */
                if (M_TRAILINGSPACE(m) < TCP_MAXOLEN) {
                        m->m_next = m_get(M_NOWAIT, MT_DATA);
                        if (m->m_next) {
                                optp = mtod(m->m_next, u_char *);
                                optm = m->m_next;
                        } else
                                incl_opts = false;
                } else {
                        optp = (u_char *) (nth + 1);
                        optm = m;
                }
        }
        if (incl_opts) {
                /* Timestamps. */
                if (tp->t_flags & TF_RCVD_TSTMP) {
                        to.to_tsval = tcp_ts_getticks() + tp->ts_offset;
                        to.to_tsecr = tp->ts_recent;
                        to.to_flags |= TOF_TS;
                }
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
                /* TCP-MD5 (RFC2385). */
                if (tp->t_flags & TF_SIGNATURE)
                        to.to_flags |= TOF_SIGNATURE;
#endif
                /* Add the options. */
                tlen += optlen = tcp_addoptions(&to, optp);

                /* Update m_len in the correct mbuf. */
                optm->m_len += optlen;
        } else
                optlen = 0;
#ifdef INET6
        if (isipv6) {
                if (uh) {
                        ulen = tlen - sizeof(struct ip6_hdr);
                        uh->uh_ulen = htons(ulen);
                }
                ip6->ip6_flow = htonl(ect << 20);
                ip6->ip6_vfc = IPV6_VERSION;
                if (port)
                        ip6->ip6_nxt = IPPROTO_UDP;
                else
                        ip6->ip6_nxt = IPPROTO_TCP;
                ip6->ip6_plen = htons(tlen - sizeof(*ip6));
        }
#endif
#if defined(INET) && defined(INET6)
        else
#endif
#ifdef INET
        {
                if (uh) {
                        ulen = tlen - sizeof(struct ip);
                        uh->uh_ulen = htons(ulen);
                }
                ip->ip_tos = ect;
                ip->ip_len = htons(tlen);
                ip->ip_ttl = V_ip_defttl;
                if (port) {
                        ip->ip_p = IPPROTO_UDP;
                } else {
                        ip->ip_p = IPPROTO_TCP;
                }
                if (V_path_mtu_discovery)
                        ip->ip_off |= htons(IP_DF);
        }
#endif
        m->m_pkthdr.len = tlen;
        m->m_pkthdr.rcvif = NULL;
#ifdef MAC
        if (inp != NULL) {
                /*
                 * Packet is associated with a socket, so allow the
                 * label of the response to reflect the socket label.
                 */
                INP_LOCK_ASSERT(inp);
                mac_inpcb_create_mbuf(inp, m);
        } else {
                /*
                 * Packet is not associated with a socket, so possibly
                 * update the label in place.
                 */
                mac_netinet_tcp_reply(m);
        }
#endif
        nth->th_seq = htonl(seq);
        nth->th_ack = htonl(ack);
        nth->th_off = (sizeof (struct tcphdr) + optlen) >> 2;
        tcp_set_flags(nth, flags);
        if (tp != NULL)
                nth->th_win = htons((u_short) (win >> tp->rcv_scale));
        else
                nth->th_win = htons((u_short)win);
        nth->th_urp = 0;

#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
        if (to.to_flags & TOF_SIGNATURE) {
                if (!TCPMD5_ENABLED() ||
                    TCPMD5_OUTPUT(m, nth, to.to_signature) != 0) {
                        m_freem(m);
                        return;
                }
        }
#endif

#ifdef INET6
        if (isipv6) {
                if (port) {
                        m->m_pkthdr.csum_flags = CSUM_UDP_IPV6;
                        m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
                        uh->uh_sum = in6_cksum_pseudo(ip6, ulen, IPPROTO_UDP, 0);
                        nth->th_sum = 0;
                } else {
                        m->m_pkthdr.csum_flags = CSUM_TCP_IPV6;
                        m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
                        nth->th_sum = in6_cksum_pseudo(ip6,
                            tlen - sizeof(struct ip6_hdr), IPPROTO_TCP, 0);
                }
                ip6->ip6_hlim = in6_selecthlim(inp, NULL);
        }
#endif /* INET6 */
#if defined(INET6) && defined(INET)
        else
#endif
#ifdef INET
        {
                if (port) {
                        uh->uh_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
                            htons(ulen + IPPROTO_UDP));
                        m->m_pkthdr.csum_flags = CSUM_UDP;
                        m->m_pkthdr.csum_data = offsetof(struct udphdr, uh_sum);
                        nth->th_sum = 0;
                } else {
                        m->m_pkthdr.csum_flags = CSUM_TCP;
                        m->m_pkthdr.csum_data = offsetof(struct tcphdr, th_sum);
                        nth->th_sum = in_pseudo(ip->ip_src.s_addr, ip->ip_dst.s_addr,
                            htons((u_short)(tlen - sizeof(struct ip) + ip->ip_p)));
                }
        }
#endif /* INET */
        TCP_PROBE3(debug__output, tp, th, m);
        if (flags & TH_RST)
                TCP_PROBE5(accept__refused, NULL, NULL, m, tp, nth);
        lgb = NULL;
        if ((tp != NULL) && (tp->t_logstate != TCP_LOG_STATE_OFF)) {
                if (INP_WLOCKED(inp)) {
                        union tcp_log_stackspecific log;
                        struct timeval tv;

                        memset(&log.u_bbr, 0, sizeof(log.u_bbr));
                        log.u_bbr.inhpts = inp->inp_in_hpts;
                        log.u_bbr.flex8 = 4;
                        log.u_bbr.pkts_out = tp->t_maxseg;
                        log.u_bbr.timeStamp = tcp_get_usecs(&tv);
                        log.u_bbr.delivered = 0;
                        lgb = tcp_log_event_(tp, nth, NULL, NULL, TCP_LOG_OUT,
                            ERRNO_UNK, 0, &log, false, NULL, NULL, 0, &tv);
                } else {
                        /*
                         * We can not log the packet, since we only own the
                         * read lock, but a write lock is needed. The read lock
                         * is not upgraded to a write lock, since only getting
                         * the read lock was done intentionally to improve the
                         * handling of SYN flooding attacks.
                         * This happens only for pure SYN segments received in
                         * the initial CLOSED state, or received in a more
                         * advanced state than listen and the UDP encapsulation
                         * port is unexpected.
                         * The incoming SYN segments do not really belong to
                         * the TCP connection and the handling does not change
                         * the state of the TCP connection. Therefore, the
                         * sending of the RST segments is not logged. Please
                         * note that also the incoming SYN segments are not
                         * logged.
                         *
                         * The following code ensures that the above description
                         * is and stays correct.
                         */
                        KASSERT((thflags & (TH_ACK|TH_SYN)) == TH_SYN &&
                            (tp->t_state == TCPS_CLOSED ||
                            (tp->t_state > TCPS_LISTEN && tp->t_port != port)),
                            ("%s: Logging of TCP segment with flags 0x%b and "
                            "UDP encapsulation port %u skipped in state %s",
                            __func__, thflags, PRINT_TH_FLAGS,
                            ntohs(port), tcpstates[tp->t_state]));
                }
        }

        if (flags & TH_ACK)
                TCPSTAT_INC(tcps_sndacks);
        else if (flags & (TH_SYN|TH_FIN|TH_RST))
                TCPSTAT_INC(tcps_sndctrl);
        TCPSTAT_INC(tcps_sndtotal);

#ifdef INET6
        if (isipv6) {
                TCP_PROBE5(send, NULL, tp, ip6, tp, nth);
                output_ret = ip6_output(m, NULL, NULL, 0, NULL, NULL, inp);
        }
#endif /* INET6 */
#if defined(INET) && defined(INET6)
        else
#endif
#ifdef INET
        {
                TCP_PROBE5(send, NULL, tp, ip, tp, nth);
                output_ret = ip_output(m, NULL, NULL, 0, NULL, inp);
        }
#endif
        if (lgb != NULL)
                lgb->tlb_errno = output_ret;
}

/*
 * Create a new TCP control block, making an empty reassembly queue and hooking
 * it to the argument protocol control block.  The `inp' parameter must have
 * come from the zone allocator set up by tcpcbstor declaration.
 */
struct tcpcb *
tcp_newtcpcb(struct inpcb *inp)
{
        struct tcpcb *tp = intotcpcb(inp);
#ifdef INET6
        int isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
#endif /* INET6 */

        /*
         * Historically allocation was done with M_ZERO.  There is a lot of
         * code that rely on that.  For now take safe approach and zero whole
         * tcpcb.  This definitely can be optimized.
         */
        bzero(&tp->t_start_zero, t_zero_size);

        /* Initialise cc_var struct for this tcpcb. */
        tp->t_ccv.type = IPPROTO_TCP;
        tp->t_ccv.ccvc.tcp = tp;
        rw_rlock(&tcp_function_lock);
        tp->t_fb = tcp_func_set_ptr;
        refcount_acquire(&tp->t_fb->tfb_refcnt);
        rw_runlock(&tcp_function_lock);
        /*
         * Use the current system default CC algorithm.
         */
        cc_attach(tp, CC_DEFAULT_ALGO());

        if (CC_ALGO(tp)->cb_init != NULL)
                if (CC_ALGO(tp)->cb_init(&tp->t_ccv, NULL) > 0) {
                        cc_detach(tp);
                        if (tp->t_fb->tfb_tcp_fb_fini)
                                (*tp->t_fb->tfb_tcp_fb_fini)(tp, 1);
                        refcount_release(&tp->t_fb->tfb_refcnt);
                        return (NULL);
                }

#ifdef TCP_HHOOK
        if (khelp_init_osd(HELPER_CLASS_TCP, &tp->t_osd)) {
                if (tp->t_fb->tfb_tcp_fb_fini)
                        (*tp->t_fb->tfb_tcp_fb_fini)(tp, 1);
                refcount_release(&tp->t_fb->tfb_refcnt);
                return (NULL);
        }
#endif

        TAILQ_INIT(&tp->t_segq);
        tp->t_maxseg =
#ifdef INET6
                isipv6 ? V_tcp_v6mssdflt :
#endif /* INET6 */
                V_tcp_mssdflt;

        callout_init_rw(&tp->t_callout, &inp->inp_lock, CALLOUT_RETURNUNLOCKED);
        for (int i = 0; i < TT_N; i++)
                tp->t_timers[i] = SBT_MAX;

        switch (V_tcp_do_rfc1323) {
                case 0:
                        break;
                default:
                case 1:
                        tp->t_flags = (TF_REQ_SCALE|TF_REQ_TSTMP);
                        break;
                case 2:
                        tp->t_flags = TF_REQ_SCALE;
                        break;
                case 3:
                        tp->t_flags = TF_REQ_TSTMP;
                        break;
        }
        if (V_tcp_do_sack)
                tp->t_flags |= TF_SACK_PERMIT;
        TAILQ_INIT(&tp->snd_holes);

        /*
         * Init srtt to TCPTV_SRTTBASE (0), so we can tell that we have no
         * rtt estimate.  Set rttvar so that srtt + 4 * rttvar gives
         * reasonable initial retransmit time.
         */
        tp->t_srtt = TCPTV_SRTTBASE;
        tp->t_rttvar = ((tcp_rexmit_initial - TCPTV_SRTTBASE) << TCP_RTTVAR_SHIFT) / 4;
        tp->t_rttmin = tcp_rexmit_min;
        tp->t_rxtcur = tcp_rexmit_initial;
        tp->snd_cwnd = TCP_MAXWIN << TCP_MAX_WINSHIFT;
        tp->snd_ssthresh = TCP_MAXWIN << TCP_MAX_WINSHIFT;
        tp->t_rcvtime = ticks;
        /*
         * IPv4 TTL initialization is necessary for an IPv6 socket as well,
         * because the socket may be bound to an IPv6 wildcard address,
         * which may match an IPv4-mapped IPv6 address.
         */
        inp->inp_ip_ttl = V_ip_defttl;
#ifdef TCPHPTS
        /*
         * If using hpts lets drop a random number in so
         * not all new connections fall on the same CPU.
         */
        inp->inp_hpts_cpu = hpts_random_cpu(inp);
#endif
#ifdef TCPPCAP
        /*
         * Init the TCP PCAP queues.
         */
        tcp_pcap_tcpcb_init(tp);
#endif
#ifdef TCP_BLACKBOX
        /* Initialize the per-TCPCB log data. */
        tcp_log_tcpcbinit(tp);
#endif
        tp->t_pacing_rate = -1;
        if (tp->t_fb->tfb_tcp_fb_init) {
                if ((*tp->t_fb->tfb_tcp_fb_init)(tp)) {
                        refcount_release(&tp->t_fb->tfb_refcnt);
                        return (NULL);
                }
        }
#ifdef STATS
        if (V_tcp_perconn_stats_enable == 1)
                tp->t_stats = stats_blob_alloc(V_tcp_perconn_stats_dflt_tpl, 0);
#endif
        if (V_tcp_do_lrd)
                tp->t_flags |= TF_LRD;

        return (tp);
}

/*
 * Drop a TCP connection, reporting
 * the specified error.  If connection is synchronized,
 * then send a RST to peer.
 */
struct tcpcb *
tcp_drop(struct tcpcb *tp, int errno)
{
        struct socket *so = tptosocket(tp);

        NET_EPOCH_ASSERT();
        INP_WLOCK_ASSERT(tptoinpcb(tp));

        if (TCPS_HAVERCVDSYN(tp->t_state)) {
                tcp_state_change(tp, TCPS_CLOSED);
                /* Don't use tcp_output() here due to possible recursion. */
                (void)tcp_output_nodrop(tp);
                TCPSTAT_INC(tcps_drops);
        } else
                TCPSTAT_INC(tcps_conndrops);
        if (errno == ETIMEDOUT && tp->t_softerror)
                errno = tp->t_softerror;
        so->so_error = errno;
        return (tcp_close(tp));
}

void
tcp_discardcb(struct tcpcb *tp)
{
        struct inpcb *inp = tptoinpcb(tp);
        struct socket *so = tptosocket(tp);
#ifdef INET6
        bool isipv6 = (inp->inp_vflag & INP_IPV6) != 0;
#endif

        INP_WLOCK_ASSERT(inp);

        tcp_timer_stop(tp);
        if (tp->t_fb->tfb_tcp_timer_stop_all) {
                tp->t_fb->tfb_tcp_timer_stop_all(tp);
        }

        /* free the reassembly queue, if any */
        tcp_reass_flush(tp);

#ifdef TCP_OFFLOAD
        /* Disconnect offload device, if any. */
        if (tp->t_flags & TF_TOE)
                tcp_offload_detach(tp);
#endif

        tcp_free_sackholes(tp);

#ifdef TCPPCAP
        /* Free the TCP PCAP queues. */
        tcp_pcap_drain(&(tp->t_inpkts));
        tcp_pcap_drain(&(tp->t_outpkts));
#endif

        /* Allow the CC algorithm to clean up after itself. */
        if (CC_ALGO(tp)->cb_destroy != NULL)
                CC_ALGO(tp)->cb_destroy(&tp->t_ccv);
        CC_DATA(tp) = NULL;
        /* Detach from the CC algorithm */
        cc_detach(tp);

#ifdef TCP_HHOOK
        khelp_destroy_osd(&tp->t_osd);
#endif
#ifdef STATS
        stats_blob_destroy(tp->t_stats);
#endif

        CC_ALGO(tp) = NULL;

#ifdef TCP_BLACKBOX
        tcp_log_tcpcbfini(tp);
#endif
        TCPSTATES_DEC(tp->t_state);
        if (tp->t_fb->tfb_tcp_fb_fini)
                (*tp->t_fb->tfb_tcp_fb_fini)(tp, 1);

        /*
         * If we got enough samples through the srtt filter,
         * save the rtt and rttvar in the routing entry.
         * 'Enough' is arbitrarily defined as 4 rtt samples.
         * 4 samples is enough for the srtt filter to converge
         * to within enough % of the correct value; fewer samples
         * and we could save a bogus rtt. The danger is not high
         * as tcp quickly recovers from everything.
         * XXX: Works very well but needs some more statistics!
         *
         * XXXRRS: Updating must be after the stack fini() since
         * that may be converting some internal representation of
         * say srtt etc into the general one used by other stacks.
         * Lets also at least protect against the so being NULL
         * as RW stated below.
         */
        if ((tp->t_rttupdated >= 4) && (so != NULL)) {
                struct hc_metrics_lite metrics;
                uint32_t ssthresh;

                bzero(&metrics, sizeof(metrics));
                /*
                 * Update the ssthresh always when the conditions below
                 * are satisfied. This gives us better new start value
                 * for the congestion avoidance for new connections.
                 * ssthresh is only set if packet loss occurred on a session.
                 *
                 * XXXRW: 'so' may be NULL here, and/or socket buffer may be
                 * being torn down.  Ideally this code would not use 'so'.
                 */
                ssthresh = tp->snd_ssthresh;
                if (ssthresh != 0 && ssthresh < so->so_snd.sb_hiwat / 2) {
                        /*
                         * convert the limit from user data bytes to
                         * packets then to packet data bytes.
                         */
                        ssthresh = (ssthresh + tp->t_maxseg / 2) / tp->t_maxseg;
                        if (ssthresh < 2)
                                ssthresh = 2;
                        ssthresh *= (tp->t_maxseg +
#ifdef INET6
                            (isipv6 ? sizeof (struct ip6_hdr) +
                            sizeof (struct tcphdr) :
#endif
                            sizeof (struct tcpiphdr)
#ifdef INET6
                            )
#endif
                            );
                } else
                        ssthresh = 0;
                metrics.rmx_ssthresh = ssthresh;

                metrics.rmx_rtt = tp->t_srtt;
                metrics.rmx_rttvar = tp->t_rttvar;
                metrics.rmx_cwnd = tp->snd_cwnd;
                metrics.rmx_sendpipe = 0;
                metrics.rmx_recvpipe = 0;

                tcp_hc_update(&inp->inp_inc, &metrics);
        }

        refcount_release(&tp->t_fb->tfb_refcnt);
}

/*
 * Attempt to close a TCP control block, marking it as dropped, and freeing
 * the socket if we hold the only reference.
 */
struct tcpcb *
tcp_close(struct tcpcb *tp)
{
        struct inpcb *inp = tptoinpcb(tp);
        struct socket *so = tptosocket(tp);

        INP_WLOCK_ASSERT(inp);

#ifdef TCP_OFFLOAD
        if (tp->t_state == TCPS_LISTEN)
                tcp_offload_listen_stop(tp);
#endif
        /*
         * This releases the TFO pending counter resource for TFO listen
         * sockets as well as passively-created TFO sockets that transition
         * from SYN_RECEIVED to CLOSED.
         */
        if (tp->t_tfo_pending) {
                tcp_fastopen_decrement_counter(tp->t_tfo_pending);
                tp->t_tfo_pending = NULL;
        }
#ifdef TCPHPTS
        tcp_hpts_remove(inp);
#endif
        in_pcbdrop(inp);
        TCPSTAT_INC(tcps_closed);
        if (tp->t_state != TCPS_CLOSED)
                tcp_state_change(tp, TCPS_CLOSED);
        KASSERT(inp->inp_socket != NULL, ("tcp_close: inp_socket NULL"));
        soisdisconnected(so);
        if (inp->inp_flags & INP_SOCKREF) {
                inp->inp_flags &= ~INP_SOCKREF;
                INP_WUNLOCK(inp);
                sorele(so);
                return (NULL);
        }
        return (tp);
}

/*
 * Notify a tcp user of an asynchronous error;
 * store error as soft error, but wake up user
 * (for now, won't do anything until can select for soft error).
 *
 * Do not wake up user since there currently is no mechanism for
 * reporting soft errors (yet - a kqueue filter may be added).
 */
static struct inpcb *
tcp_notify(struct inpcb *inp, int error)
{
        struct tcpcb *tp;

        INP_WLOCK_ASSERT(inp);

        tp = intotcpcb(inp);
        KASSERT(tp != NULL, ("tcp_notify: tp == NULL"));

        /*
         * Ignore some errors if we are hooked up.
         * If connection hasn't completed, has retransmitted several times,
         * and receives a second error, give up now.  This is better
         * than waiting a long time to establish a connection that
         * can never complete.
         */
        if (tp->t_state == TCPS_ESTABLISHED &&
            (error == EHOSTUNREACH || error == ENETUNREACH ||
             error == EHOSTDOWN)) {
                if (inp->inp_route.ro_nh) {
                        NH_FREE(inp->inp_route.ro_nh);
                        inp->inp_route.ro_nh = (struct nhop_object *)NULL;
                }
                return (inp);
        } else if (tp->t_state < TCPS_ESTABLISHED && tp->t_rxtshift > 3 &&
            tp->t_softerror) {
                tp = tcp_drop(tp, error);
                if (tp != NULL)
                        return (inp);
                else
                        return (NULL);
        } else {
                tp->t_softerror = error;
                return (inp);
        }
#if 0
        wakeup( &so->so_timeo);
        sorwakeup(so);
        sowwakeup(so);
#endif
}

static int
tcp_pcblist(SYSCTL_HANDLER_ARGS)
{
        struct inpcb_iterator inpi = INP_ALL_ITERATOR(&V_tcbinfo,
            INPLOOKUP_RLOCKPCB);
        struct xinpgen xig;
        struct inpcb *inp;
        int error;

        if (req->newptr != NULL)
                return (EPERM);

        if (req->oldptr == NULL) {
                int n;

                n = V_tcbinfo.ipi_count +
                    counter_u64_fetch(V_tcps_states[TCPS_SYN_RECEIVED]);
                n += imax(n / 8, 10);
                req->oldidx = 2 * (sizeof xig) + n * sizeof(struct xtcpcb);
                return (0);
        }

        if ((error = sysctl_wire_old_buffer(req, 0)) != 0)
                return (error);

        bzero(&xig, sizeof(xig));
        xig.xig_len = sizeof xig;
        xig.xig_count = V_tcbinfo.ipi_count +
            counter_u64_fetch(V_tcps_states[TCPS_SYN_RECEIVED]);
        xig.xig_gen = V_tcbinfo.ipi_gencnt;
        xig.xig_sogen = so_gencnt;
        error = SYSCTL_OUT(req, &xig, sizeof xig);
        if (error)
                return (error);

        error = syncache_pcblist(req);
        if (error)
                return (error);

        while ((inp = inp_next(&inpi)) != NULL) {
                if (inp->inp_gencnt <= xig.xig_gen &&
                    cr_canseeinpcb(req->td->td_ucred, inp) == 0) {
                        struct xtcpcb xt;

                        tcp_inptoxtp(inp, &xt);
                        error = SYSCTL_OUT(req, &xt, sizeof xt);
                        if (error) {
                                INP_RUNLOCK(inp);
                                break;
                        } else
                                continue;
                }
        }

        if (!error) {
                /*
                 * Give the user an updated idea of our state.
                 * If the generation differs from what we told
                 * her before, she knows that something happened
                 * while we were processing this request, and it
                 * might be necessary to retry.
                 */
                xig.xig_gen = V_tcbinfo.ipi_gencnt;
                xig.xig_sogen = so_gencnt;
                xig.xig_count = V_tcbinfo.ipi_count +
                    counter_u64_fetch(V_tcps_states[TCPS_SYN_RECEIVED]);
                error = SYSCTL_OUT(req, &xig, sizeof xig);
        }

        return (error);
}

SYSCTL_PROC(_net_inet_tcp, TCPCTL_PCBLIST, pcblist,
    CTLTYPE_OPAQUE | CTLFLAG_RD | CTLFLAG_NEEDGIANT,
    NULL, 0, tcp_pcblist, "S,xtcpcb",
    "List of active TCP connections");

#ifdef INET
static int
tcp_getcred(SYSCTL_HANDLER_ARGS)
{
        struct xucred xuc;
        struct sockaddr_in addrs[2];
        struct epoch_tracker et;
        struct inpcb *inp;
        int error;

        error = priv_check(req->td, PRIV_NETINET_GETCRED);
        if (error)
                return (error);
        error = SYSCTL_IN(req, addrs, sizeof(addrs));
        if (error)
                return (error);
        NET_EPOCH_ENTER(et);
        inp = in_pcblookup(&V_tcbinfo, addrs[1].sin_addr, addrs[1].sin_port,
            addrs[0].sin_addr, addrs[0].sin_port, INPLOOKUP_RLOCKPCB, NULL);
        NET_EPOCH_EXIT(et);
        if (inp != NULL) {
                if (error == 0)
                        error = cr_canseeinpcb(req->td->td_ucred, inp);
                if (error == 0)
                        cru2x(inp->inp_cred, &xuc);
                INP_RUNLOCK(inp);
        } else
                error = ENOENT;
        if (error == 0)
                error = SYSCTL_OUT(req, &xuc, sizeof(struct xucred));
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, getcred,
    CTLTYPE_OPAQUE | CTLFLAG_RW | CTLFLAG_PRISON | CTLFLAG_NEEDGIANT,
    0, 0, tcp_getcred, "S,xucred",
    "Get the xucred of a TCP connection");
#endif /* INET */

#ifdef INET6
static int
tcp6_getcred(SYSCTL_HANDLER_ARGS)
{
        struct epoch_tracker et;
        struct xucred xuc;
        struct sockaddr_in6 addrs[2];
        struct inpcb *inp;
        int error;
#ifdef INET
        int mapped = 0;
#endif

        error = priv_check(req->td, PRIV_NETINET_GETCRED);
        if (error)
                return (error);
        error = SYSCTL_IN(req, addrs, sizeof(addrs));
        if (error)
                return (error);
        if ((error = sa6_embedscope(&addrs[0], V_ip6_use_defzone)) != 0 ||
            (error = sa6_embedscope(&addrs[1], V_ip6_use_defzone)) != 0) {
                return (error);
        }
        if (IN6_IS_ADDR_V4MAPPED(&addrs[0].sin6_addr)) {
#ifdef INET
                if (IN6_IS_ADDR_V4MAPPED(&addrs[1].sin6_addr))
                        mapped = 1;
                else
#endif
                        return (EINVAL);
        }

        NET_EPOCH_ENTER(et);
#ifdef INET
        if (mapped == 1)
                inp = in_pcblookup(&V_tcbinfo,
                        *(struct in_addr *)&addrs[1].sin6_addr.s6_addr[12],
                        addrs[1].sin6_port,
                        *(struct in_addr *)&addrs[0].sin6_addr.s6_addr[12],
                        addrs[0].sin6_port, INPLOOKUP_RLOCKPCB, NULL);
        else
#endif
                inp = in6_pcblookup(&V_tcbinfo,
                        &addrs[1].sin6_addr, addrs[1].sin6_port,
                        &addrs[0].sin6_addr, addrs[0].sin6_port,
                        INPLOOKUP_RLOCKPCB, NULL);
        NET_EPOCH_EXIT(et);
        if (inp != NULL) {
                if (error == 0)
                        error = cr_canseeinpcb(req->td->td_ucred, inp);
                if (error == 0)
                        cru2x(inp->inp_cred, &xuc);
                INP_RUNLOCK(inp);
        } else
                error = ENOENT;
        if (error == 0)
                error = SYSCTL_OUT(req, &xuc, sizeof(struct xucred));
        return (error);
}

SYSCTL_PROC(_net_inet6_tcp6, OID_AUTO, getcred,
    CTLTYPE_OPAQUE | CTLFLAG_RW | CTLFLAG_PRISON | CTLFLAG_NEEDGIANT,
    0, 0, tcp6_getcred, "S,xucred",
    "Get the xucred of a TCP6 connection");
#endif /* INET6 */

#ifdef INET
/* Path MTU to try next when a fragmentation-needed message is received. */
static inline int
tcp_next_pmtu(const struct icmp *icp, const struct ip *ip)
{
        int mtu = ntohs(icp->icmp_nextmtu);

        /* If no alternative MTU was proposed, try the next smaller one. */
        if (!mtu)
                mtu = ip_next_mtu(ntohs(ip->ip_len), 1);
        if (mtu < V_tcp_minmss + sizeof(struct tcpiphdr))
                mtu = V_tcp_minmss + sizeof(struct tcpiphdr);

        return (mtu);
}

static void
tcp_ctlinput_with_port(struct icmp *icp, uint16_t port)
{
        struct ip *ip;
        struct tcphdr *th;
        struct inpcb *inp;
        struct tcpcb *tp;
        struct inpcb *(*notify)(struct inpcb *, int);
        struct in_conninfo inc;
        tcp_seq icmp_tcp_seq;
        int errno, mtu;

        errno = icmp_errmap(icp);
        switch (errno) {
        case 0:
                return;
        case EMSGSIZE:
                notify = tcp_mtudisc_notify;
                break;
        case ECONNREFUSED:
                if (V_icmp_may_rst)
                        notify = tcp_drop_syn_sent;
                else
                        notify = tcp_notify;
                break;
        case EHOSTUNREACH:
                if (V_icmp_may_rst && icp->icmp_type == ICMP_TIMXCEED)
                        notify = tcp_drop_syn_sent;
                else
                        notify = tcp_notify;
                break;
        default:
                notify = tcp_notify;
        }

        ip = &icp->icmp_ip;
        th = (struct tcphdr *)((caddr_t)ip + (ip->ip_hl << 2));
        icmp_tcp_seq = th->th_seq;
        inp = in_pcblookup(&V_tcbinfo, ip->ip_dst, th->th_dport, ip->ip_src,
            th->th_sport, INPLOOKUP_WLOCKPCB, NULL);
        if (inp != NULL)  {
                tp = intotcpcb(inp);
#ifdef TCP_OFFLOAD
                if (tp->t_flags & TF_TOE && errno == EMSGSIZE) {
                        /*
                         * MTU discovery for offloaded connections.  Let
                         * the TOE driver verify seq# and process it.
                         */
                        mtu = tcp_next_pmtu(icp, ip);
                        tcp_offload_pmtu_update(tp, icmp_tcp_seq, mtu);
                        goto out;
                }
#endif
                if (tp->t_port != port)
                        goto out;
                if (SEQ_GEQ(ntohl(icmp_tcp_seq), tp->snd_una) &&
                    SEQ_LT(ntohl(icmp_tcp_seq), tp->snd_max)) {
                        if (errno == EMSGSIZE) {
                                /*
                                 * MTU discovery: we got a needfrag and
                                 * will potentially try a lower MTU.
                                 */
                                mtu = tcp_next_pmtu(icp, ip);

                                /*
                                 * Only process the offered MTU if it
                                 * is smaller than the current one.
                                 */
                                if (mtu < tp->t_maxseg +
                                    sizeof(struct tcpiphdr)) {
                                        bzero(&inc, sizeof(inc));
                                        inc.inc_faddr = ip->ip_dst;
                                        inc.inc_fibnum =
                                            inp->inp_inc.inc_fibnum;
                                        tcp_hc_updatemtu(&inc, mtu);
                                        inp = tcp_mtudisc(inp, mtu);
                                }
                        } else
                                inp = (*notify)(inp, errno);
                }
        } else {
                bzero(&inc, sizeof(inc));
                inc.inc_fport = th->th_dport;
                inc.inc_lport = th->th_sport;
                inc.inc_faddr = ip->ip_dst;
                inc.inc_laddr = ip->ip_src;
                syncache_unreach(&inc, icmp_tcp_seq, port);
        }
out:
        if (inp != NULL)
                INP_WUNLOCK(inp);
}

static void
tcp_ctlinput(struct icmp *icmp)
{
        tcp_ctlinput_with_port(icmp, htons(0));
}

static void
tcp_ctlinput_viaudp(udp_tun_icmp_param_t param)
{
        /* Its a tunneled TCP over UDP icmp */
        struct icmp *icmp = param.icmp;
        struct ip *outer_ip, *inner_ip;
        struct udphdr *udp;
        struct tcphdr *th, ttemp;
        int i_hlen, o_len;
        uint16_t port;

        outer_ip = (struct ip *)((caddr_t)icmp - sizeof(struct ip));
        inner_ip = &icmp->icmp_ip;
        i_hlen = inner_ip->ip_hl << 2;
        o_len = ntohs(outer_ip->ip_len);
        if (o_len <
            (sizeof(struct ip) + 8 + i_hlen + sizeof(struct udphdr) + offsetof(struct tcphdr, th_ack))) {
                /* Not enough data present */
                return;
        }
        /* Ok lets strip out the inner udphdr header by copying up on top of it the tcp hdr */
        udp = (struct udphdr *)(((caddr_t)inner_ip) + i_hlen);
        if (ntohs(udp->uh_sport) != V_tcp_udp_tunneling_port) {
                return;
        }
        port = udp->uh_dport;
        th = (struct tcphdr *)(udp + 1);
        memcpy(&ttemp, th, sizeof(struct tcphdr));
        memcpy(udp, &ttemp, sizeof(struct tcphdr));
        /* Now adjust down the size of the outer IP header */
        o_len -= sizeof(struct udphdr);
        outer_ip->ip_len = htons(o_len);
        /* Now call in to the normal handling code */
        tcp_ctlinput_with_port(icmp, port);
}
#endif /* INET */

#ifdef INET6
static inline int
tcp6_next_pmtu(const struct icmp6_hdr *icmp6)
{
        int mtu = ntohl(icmp6->icmp6_mtu);

        /*
         * If no alternative MTU was proposed, or the proposed MTU was too
         * small, set to the min.
         */
        if (mtu < IPV6_MMTU)
                mtu = IPV6_MMTU - 8;    /* XXXNP: what is the adjustment for? */
        return (mtu);
}

static void
tcp6_ctlinput_with_port(struct ip6ctlparam *ip6cp, uint16_t port)
{
        struct in6_addr *dst;
        struct inpcb *(*notify)(struct inpcb *, int);
        struct ip6_hdr *ip6;
        struct mbuf *m;
        struct inpcb *inp;
        struct tcpcb *tp;
        struct icmp6_hdr *icmp6;
        struct in_conninfo inc;
        struct tcp_ports {
                uint16_t th_sport;
                uint16_t th_dport;
        } t_ports;
        tcp_seq icmp_tcp_seq;
        unsigned int mtu;
        unsigned int off;
        int errno;

        icmp6 = ip6cp->ip6c_icmp6;
        m = ip6cp->ip6c_m;
        ip6 = ip6cp->ip6c_ip6;
        off = ip6cp->ip6c_off;
        dst = &ip6cp->ip6c_finaldst->sin6_addr;

        errno = icmp6_errmap(icmp6);
        switch (errno) {
        case 0:
                return;
        case EMSGSIZE:
                notify = tcp_mtudisc_notify;
                break;
        case ECONNREFUSED:
                if (V_icmp_may_rst)
                        notify = tcp_drop_syn_sent;
                else
                        notify = tcp_notify;
                break;
        case EHOSTUNREACH:
                /*
                 * There are only four ICMPs that may reset connection:
                 * - administratively prohibited
                 * - port unreachable
                 * - time exceeded in transit
                 * - unknown next header
                 */
                if (V_icmp_may_rst &&
                    ((icmp6->icmp6_type == ICMP6_DST_UNREACH &&
                     (icmp6->icmp6_code == ICMP6_DST_UNREACH_ADMIN ||
                      icmp6->icmp6_code == ICMP6_DST_UNREACH_NOPORT)) ||
                    (icmp6->icmp6_type == ICMP6_TIME_EXCEEDED &&
                      icmp6->icmp6_code == ICMP6_TIME_EXCEED_TRANSIT) ||
                    (icmp6->icmp6_type == ICMP6_PARAM_PROB &&
                      icmp6->icmp6_code == ICMP6_PARAMPROB_NEXTHEADER)))
                        notify = tcp_drop_syn_sent;
                else
                        notify = tcp_notify;
                break;
        default:
                notify = tcp_notify;
        }

        /* Check if we can safely get the ports from the tcp hdr */
        if (m == NULL ||
            (m->m_pkthdr.len <
                (int32_t) (off + sizeof(struct tcp_ports)))) {
                return;
        }
        bzero(&t_ports, sizeof(struct tcp_ports));
        m_copydata(m, off, sizeof(struct tcp_ports), (caddr_t)&t_ports);
        inp = in6_pcblookup(&V_tcbinfo, &ip6->ip6_dst, t_ports.th_dport,
            &ip6->ip6_src, t_ports.th_sport, INPLOOKUP_WLOCKPCB, NULL);
        off += sizeof(struct tcp_ports);
        if (m->m_pkthdr.len < (int32_t) (off + sizeof(tcp_seq))) {
                goto out;
        }
        m_copydata(m, off, sizeof(tcp_seq), (caddr_t)&icmp_tcp_seq);
        if (inp != NULL)  {
                tp = intotcpcb(inp);
#ifdef TCP_OFFLOAD
                if (tp->t_flags & TF_TOE && errno == EMSGSIZE) {
                        /* MTU discovery for offloaded connections. */
                        mtu = tcp6_next_pmtu(icmp6);
                        tcp_offload_pmtu_update(tp, icmp_tcp_seq, mtu);
                        goto out;
                }
#endif
                if (tp->t_port != port)
                        goto out;
                if (SEQ_GEQ(ntohl(icmp_tcp_seq), tp->snd_una) &&
                    SEQ_LT(ntohl(icmp_tcp_seq), tp->snd_max)) {
                        if (errno == EMSGSIZE) {
                                /*
                                 * MTU discovery:
                                 * If we got a needfrag set the MTU
                                 * in the route to the suggested new
                                 * value (if given) and then notify.
                                 */
                                mtu = tcp6_next_pmtu(icmp6);

                                bzero(&inc, sizeof(inc));
                                inc.inc_fibnum = M_GETFIB(m);
                                inc.inc_flags |= INC_ISIPV6;
                                inc.inc6_faddr = *dst;
                                if (in6_setscope(&inc.inc6_faddr,
                                        m->m_pkthdr.rcvif, NULL))
                                        goto out;
                                /*
                                 * Only process the offered MTU if it
                                 * is smaller than the current one.
                                 */
                                if (mtu < tp->t_maxseg +
                                    sizeof (struct tcphdr) +
                                    sizeof (struct ip6_hdr)) {
                                        tcp_hc_updatemtu(&inc, mtu);
                                        tcp_mtudisc(inp, mtu);
                                        ICMP6STAT_INC(icp6s_pmtuchg);
                                }
                        } else
                                inp = (*notify)(inp, errno);
                }
        } else {
                bzero(&inc, sizeof(inc));
                inc.inc_fibnum = M_GETFIB(m);
                inc.inc_flags |= INC_ISIPV6;
                inc.inc_fport = t_ports.th_dport;
                inc.inc_lport = t_ports.th_sport;
                inc.inc6_faddr = *dst;
                inc.inc6_laddr = ip6->ip6_src;
                syncache_unreach(&inc, icmp_tcp_seq, port);
        }
out:
        if (inp != NULL)
                INP_WUNLOCK(inp);
}

static void
tcp6_ctlinput(struct ip6ctlparam *ctl)
{
        tcp6_ctlinput_with_port(ctl, htons(0));
}

static void
tcp6_ctlinput_viaudp(udp_tun_icmp_param_t param)
{
        struct ip6ctlparam *ip6cp = param.ip6cp;
        struct mbuf *m;
        struct udphdr *udp;
        uint16_t port;

        m = m_pulldown(ip6cp->ip6c_m, ip6cp->ip6c_off, sizeof(struct udphdr), NULL);
        if (m == NULL) {
                return;
        }
        udp = mtod(m, struct udphdr *);
        if (ntohs(udp->uh_sport) != V_tcp_udp_tunneling_port) {
                return;
        }
        port = udp->uh_dport;
        m_adj(m, sizeof(struct udphdr));
        if ((m->m_flags & M_PKTHDR) == 0) {
                ip6cp->ip6c_m->m_pkthdr.len -= sizeof(struct udphdr);
        }
        /* Now call in to the normal handling code */
        tcp6_ctlinput_with_port(ip6cp, port);
}

#endif /* INET6 */

static uint32_t
tcp_keyed_hash(struct in_conninfo *inc, u_char *key, u_int len)
{
        SIPHASH_CTX ctx;
        uint32_t hash[2];

        KASSERT(len >= SIPHASH_KEY_LENGTH,
            ("%s: keylen %u too short ", __func__, len));
        SipHash24_Init(&ctx);
        SipHash_SetKey(&ctx, (uint8_t *)key);
        SipHash_Update(&ctx, &inc->inc_fport, sizeof(uint16_t));
        SipHash_Update(&ctx, &inc->inc_lport, sizeof(uint16_t));
        switch (inc->inc_flags & INC_ISIPV6) {
#ifdef INET
        case 0:
                SipHash_Update(&ctx, &inc->inc_faddr, sizeof(struct in_addr));
                SipHash_Update(&ctx, &inc->inc_laddr, sizeof(struct in_addr));
                break;
#endif
#ifdef INET6
        case INC_ISIPV6:
                SipHash_Update(&ctx, &inc->inc6_faddr, sizeof(struct in6_addr));
                SipHash_Update(&ctx, &inc->inc6_laddr, sizeof(struct in6_addr));
                break;
#endif
        }
        SipHash_Final((uint8_t *)hash, &ctx);

        return (hash[0] ^ hash[1]);
}

uint32_t
tcp_new_ts_offset(struct in_conninfo *inc)
{
        struct in_conninfo inc_store, *local_inc;

        if (!V_tcp_ts_offset_per_conn) {
                memcpy(&inc_store, inc, sizeof(struct in_conninfo));
                inc_store.inc_lport = 0;
                inc_store.inc_fport = 0;
                local_inc = &inc_store;
        } else {
                local_inc = inc;
        }
        return (tcp_keyed_hash(local_inc, V_ts_offset_secret,
            sizeof(V_ts_offset_secret)));
}

/*
 * Following is where TCP initial sequence number generation occurs.
 *
 * There are two places where we must use initial sequence numbers:
 * 1.  In SYN-ACK packets.
 * 2.  In SYN packets.
 *
 * All ISNs for SYN-ACK packets are generated by the syncache.  See
 * tcp_syncache.c for details.
 *
 * The ISNs in SYN packets must be monotonic; TIME_WAIT recycling
 * depends on this property.  In addition, these ISNs should be
 * unguessable so as to prevent connection hijacking.  To satisfy
 * the requirements of this situation, the algorithm outlined in
 * RFC 1948 is used, with only small modifications.
 *
 * Implementation details:
 *
 * Time is based off the system timer, and is corrected so that it
 * increases by one megabyte per second.  This allows for proper
 * recycling on high speed LANs while still leaving over an hour
 * before rollover.
 *
 * As reading the *exact* system time is too expensive to be done
 * whenever setting up a TCP connection, we increment the time
 * offset in two ways.  First, a small random positive increment
 * is added to isn_offset for each connection that is set up.
 * Second, the function tcp_isn_tick fires once per clock tick
 * and increments isn_offset as necessary so that sequence numbers
 * are incremented at approximately ISN_BYTES_PER_SECOND.  The
 * random positive increments serve only to ensure that the same
 * exact sequence number is never sent out twice (as could otherwise
 * happen when a port is recycled in less than the system tick
 * interval.)
 *
 * net.inet.tcp.isn_reseed_interval controls the number of seconds
 * between seeding of isn_secret.  This is normally set to zero,
 * as reseeding should not be necessary.
 *
 * Locking of the global variables isn_secret, isn_last_reseed, isn_offset,
 * isn_offset_old, and isn_ctx is performed using the ISN lock.  In
 * general, this means holding an exclusive (write) lock.
 */

#define ISN_BYTES_PER_SECOND 1048576
#define ISN_STATIC_INCREMENT 4096
#define ISN_RANDOM_INCREMENT (4096 - 1)
#define ISN_SECRET_LENGTH    SIPHASH_KEY_LENGTH

VNET_DEFINE_STATIC(u_char, isn_secret[ISN_SECRET_LENGTH]);
VNET_DEFINE_STATIC(int, isn_last);
VNET_DEFINE_STATIC(int, isn_last_reseed);
VNET_DEFINE_STATIC(u_int32_t, isn_offset);
VNET_DEFINE_STATIC(u_int32_t, isn_offset_old);

#define V_isn_secret                    VNET(isn_secret)
#define V_isn_last                      VNET(isn_last)
#define V_isn_last_reseed               VNET(isn_last_reseed)
#define V_isn_offset                    VNET(isn_offset)
#define V_isn_offset_old                VNET(isn_offset_old)

tcp_seq
tcp_new_isn(struct in_conninfo *inc)
{
        tcp_seq new_isn;
        u_int32_t projected_offset;

        ISN_LOCK();
        /* Seed if this is the first use, reseed if requested. */
        if ((V_isn_last_reseed == 0) || ((V_tcp_isn_reseed_interval > 0) &&
             (((u_int)V_isn_last_reseed + (u_int)V_tcp_isn_reseed_interval*hz)
                < (u_int)ticks))) {
                arc4rand(&V_isn_secret, sizeof(V_isn_secret), 0);
                V_isn_last_reseed = ticks;
        }

        /* Compute the hash and return the ISN. */
        new_isn = (tcp_seq)tcp_keyed_hash(inc, V_isn_secret,
            sizeof(V_isn_secret));
        V_isn_offset += ISN_STATIC_INCREMENT +
                (arc4random() & ISN_RANDOM_INCREMENT);
        if (ticks != V_isn_last) {
                projected_offset = V_isn_offset_old +
                    ISN_BYTES_PER_SECOND / hz * (ticks - V_isn_last);
                if (SEQ_GT(projected_offset, V_isn_offset))
                        V_isn_offset = projected_offset;
                V_isn_offset_old = V_isn_offset;
                V_isn_last = ticks;
        }
        new_isn += V_isn_offset;
        ISN_UNLOCK();
        return (new_isn);
}

/*
 * When a specific ICMP unreachable message is received and the
 * connection state is SYN-SENT, drop the connection.  This behavior
 * is controlled by the icmp_may_rst sysctl.
 */
static struct inpcb *
tcp_drop_syn_sent(struct inpcb *inp, int errno)
{
        struct tcpcb *tp;

        NET_EPOCH_ASSERT();
        INP_WLOCK_ASSERT(inp);

        tp = intotcpcb(inp);
        if (tp->t_state != TCPS_SYN_SENT)
                return (inp);

        if (IS_FASTOPEN(tp->t_flags))
                tcp_fastopen_disable_path(tp);

        tp = tcp_drop(tp, errno);
        if (tp != NULL)
                return (inp);
        else
                return (NULL);
}

/*
 * When `need fragmentation' ICMP is received, update our idea of the MSS
 * based on the new value. Also nudge TCP to send something, since we
 * know the packet we just sent was dropped.
 * This duplicates some code in the tcp_mss() function in tcp_input.c.
 */
static struct inpcb *
tcp_mtudisc_notify(struct inpcb *inp, int error)
{

        return (tcp_mtudisc(inp, -1));
}

static struct inpcb *
tcp_mtudisc(struct inpcb *inp, int mtuoffer)
{
        struct tcpcb *tp;
        struct socket *so;

        INP_WLOCK_ASSERT(inp);

        tp = intotcpcb(inp);
        KASSERT(tp != NULL, ("tcp_mtudisc: tp == NULL"));

        tcp_mss_update(tp, -1, mtuoffer, NULL, NULL);

        so = inp->inp_socket;
        SOCKBUF_LOCK(&so->so_snd);
        /* If the mss is larger than the socket buffer, decrease the mss. */
        if (so->so_snd.sb_hiwat < tp->t_maxseg)
                tp->t_maxseg = so->so_snd.sb_hiwat;
        SOCKBUF_UNLOCK(&so->so_snd);

        TCPSTAT_INC(tcps_mturesent);
        tp->t_rtttime = 0;
        tp->snd_nxt = tp->snd_una;
        tcp_free_sackholes(tp);
        tp->snd_recover = tp->snd_max;
        if (tp->t_flags & TF_SACK_PERMIT)
                EXIT_FASTRECOVERY(tp->t_flags);
        if (tp->t_fb->tfb_tcp_mtu_chg != NULL) {
                /*
                 * Conceptually the snd_nxt setting
                 * and freeing sack holes should
                 * be done by the default stacks
                 * own tfb_tcp_mtu_chg().
                 */
                tp->t_fb->tfb_tcp_mtu_chg(tp);
        }
        if (tcp_output(tp) < 0)
                return (NULL);
        else
                return (inp);
}

#ifdef INET
/*
 * Look-up the routing entry to the peer of this inpcb.  If no route
 * is found and it cannot be allocated, then return 0.  This routine
 * is called by TCP routines that access the rmx structure and by
 * tcp_mss_update to get the peer/interface MTU.
 */
uint32_t
tcp_maxmtu(struct in_conninfo *inc, struct tcp_ifcap *cap)
{
        struct nhop_object *nh;
        struct ifnet *ifp;
        uint32_t maxmtu = 0;

        KASSERT(inc != NULL, ("tcp_maxmtu with NULL in_conninfo pointer"));

        if (inc->inc_faddr.s_addr != INADDR_ANY) {
                nh = fib4_lookup(inc->inc_fibnum, inc->inc_faddr, 0, NHR_NONE, 0);
                if (nh == NULL)
                        return (0);

                ifp = nh->nh_ifp;
                maxmtu = nh->nh_mtu;

                /* Report additional interface capabilities. */
                if (cap != NULL) {
                        if (ifp->if_capenable & IFCAP_TSO4 &&
                            ifp->if_hwassist & CSUM_TSO) {
                                cap->ifcap |= CSUM_TSO;
                                cap->tsomax = ifp->if_hw_tsomax;
                                cap->tsomaxsegcount = ifp->if_hw_tsomaxsegcount;
                                cap->tsomaxsegsize = ifp->if_hw_tsomaxsegsize;
                        }
                }
        }
        return (maxmtu);
}
#endif /* INET */

#ifdef INET6
uint32_t
tcp_maxmtu6(struct in_conninfo *inc, struct tcp_ifcap *cap)
{
        struct nhop_object *nh;
        struct in6_addr dst6;
        uint32_t scopeid;
        struct ifnet *ifp;
        uint32_t maxmtu = 0;

        KASSERT(inc != NULL, ("tcp_maxmtu6 with NULL in_conninfo pointer"));

        if (inc->inc_flags & INC_IPV6MINMTU)
                return (IPV6_MMTU);

        if (!IN6_IS_ADDR_UNSPECIFIED(&inc->inc6_faddr)) {
                in6_splitscope(&inc->inc6_faddr, &dst6, &scopeid);
                nh = fib6_lookup(inc->inc_fibnum, &dst6, scopeid, NHR_NONE, 0);
                if (nh == NULL)
                        return (0);

                ifp = nh->nh_ifp;
                maxmtu = nh->nh_mtu;

                /* Report additional interface capabilities. */
                if (cap != NULL) {
                        if (ifp->if_capenable & IFCAP_TSO6 &&
                            ifp->if_hwassist & CSUM_TSO) {
                                cap->ifcap |= CSUM_TSO;
                                cap->tsomax = ifp->if_hw_tsomax;
                                cap->tsomaxsegcount = ifp->if_hw_tsomaxsegcount;
                                cap->tsomaxsegsize = ifp->if_hw_tsomaxsegsize;
                        }
                }
        }

        return (maxmtu);
}

/*
 * Handle setsockopt(IPV6_USE_MIN_MTU) by a TCP stack.
 *
 * XXXGL: we are updating inpcb here with INC_IPV6MINMTU flag.
 * The right place to do that is ip6_setpktopt() that has just been
 * executed.  By the way it just filled ip6po_minmtu for us.
 */
void
tcp6_use_min_mtu(struct tcpcb *tp)
{
        struct inpcb *inp = tptoinpcb(tp);

        INP_WLOCK_ASSERT(inp);
        /*
         * In case of the IPV6_USE_MIN_MTU socket
         * option, the INC_IPV6MINMTU flag to announce
         * a corresponding MSS during the initial
         * handshake.  If the TCP connection is not in
         * the front states, just reduce the MSS being
         * used.  This avoids the sending of TCP
         * segments which will be fragmented at the
         * IPv6 layer.
         */
        inp->inp_inc.inc_flags |= INC_IPV6MINMTU;
        if ((tp->t_state >= TCPS_SYN_SENT) &&
            (inp->inp_inc.inc_flags & INC_ISIPV6)) {
                struct ip6_pktopts *opt;

                opt = inp->in6p_outputopts;
                if (opt != NULL && opt->ip6po_minmtu == IP6PO_MINMTU_ALL &&
                    tp->t_maxseg > TCP6_MSS)
                        tp->t_maxseg = TCP6_MSS;
        }
}
#endif /* INET6 */

/*
 * Calculate effective SMSS per RFC5681 definition for a given TCP
 * connection at its current state, taking into account SACK and etc.
 */
u_int
tcp_maxseg(const struct tcpcb *tp)
{
        u_int optlen;

        if (tp->t_flags & TF_NOOPT)
                return (tp->t_maxseg);

        /*
         * Here we have a simplified code from tcp_addoptions(),
         * without a proper loop, and having most of paddings hardcoded.
         * We might make mistakes with padding here in some edge cases,
         * but this is harmless, since result of tcp_maxseg() is used
         * only in cwnd and ssthresh estimations.
         */
        if (TCPS_HAVEESTABLISHED(tp->t_state)) {
                if (tp->t_flags & TF_RCVD_TSTMP)
                        optlen = TCPOLEN_TSTAMP_APPA;
                else
                        optlen = 0;
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
                if (tp->t_flags & TF_SIGNATURE)
                        optlen += PADTCPOLEN(TCPOLEN_SIGNATURE);
#endif
                if ((tp->t_flags & TF_SACK_PERMIT) && tp->rcv_numsacks > 0) {
                        optlen += TCPOLEN_SACKHDR;
                        optlen += tp->rcv_numsacks * TCPOLEN_SACK;
                        optlen = PADTCPOLEN(optlen);
                }
        } else {
                if (tp->t_flags & TF_REQ_TSTMP)
                        optlen = TCPOLEN_TSTAMP_APPA;
                else
                        optlen = PADTCPOLEN(TCPOLEN_MAXSEG);
                if (tp->t_flags & TF_REQ_SCALE)
                        optlen += PADTCPOLEN(TCPOLEN_WINDOW);
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
                if (tp->t_flags & TF_SIGNATURE)
                        optlen += PADTCPOLEN(TCPOLEN_SIGNATURE);
#endif
                if (tp->t_flags & TF_SACK_PERMIT)
                        optlen += PADTCPOLEN(TCPOLEN_SACK_PERMITTED);
        }
#undef PAD
        optlen = min(optlen, TCP_MAXOLEN);
        return (tp->t_maxseg - optlen);
}


u_int
tcp_fixed_maxseg(const struct tcpcb *tp)
{
        int optlen;

        if (tp->t_flags & TF_NOOPT)
                return (tp->t_maxseg);

        /*
         * Here we have a simplified code from tcp_addoptions(),
         * without a proper loop, and having most of paddings hardcoded.
         * We only consider fixed options that we would send every
         * time I.e. SACK is not considered. This is important
         * for cc modules to figure out what the modulo of the
         * cwnd should be.
         */
#define PAD(len)        ((((len) / 4) + !!((len) % 4)) * 4)
        if (TCPS_HAVEESTABLISHED(tp->t_state)) {
                if (tp->t_flags & TF_RCVD_TSTMP)
                        optlen = TCPOLEN_TSTAMP_APPA;
                else
                        optlen = 0;
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
                if (tp->t_flags & TF_SIGNATURE)
                        optlen += PAD(TCPOLEN_SIGNATURE);
#endif
        } else {
                if (tp->t_flags & TF_REQ_TSTMP)
                        optlen = TCPOLEN_TSTAMP_APPA;
                else
                        optlen = PAD(TCPOLEN_MAXSEG);
                if (tp->t_flags & TF_REQ_SCALE)
                        optlen += PAD(TCPOLEN_WINDOW);
#if defined(IPSEC_SUPPORT) || defined(TCP_SIGNATURE)
                if (tp->t_flags & TF_SIGNATURE)
                        optlen += PAD(TCPOLEN_SIGNATURE);
#endif
                if (tp->t_flags & TF_SACK_PERMIT)
                        optlen += PAD(TCPOLEN_SACK_PERMITTED);
        }
#undef PAD
        optlen = min(optlen, TCP_MAXOLEN);
        return (tp->t_maxseg - optlen);
}



static int
sysctl_drop(SYSCTL_HANDLER_ARGS)
{
        /* addrs[0] is a foreign socket, addrs[1] is a local one. */
        struct sockaddr_storage addrs[2];
        struct inpcb *inp;
        struct tcpcb *tp;
#ifdef INET
        struct sockaddr_in *fin = NULL, *lin = NULL;
#endif
        struct epoch_tracker et;
#ifdef INET6
        struct sockaddr_in6 *fin6, *lin6;
#endif
        int error;

        inp = NULL;
#ifdef INET6
        fin6 = lin6 = NULL;
#endif
        error = 0;

        if (req->oldptr != NULL || req->oldlen != 0)
                return (EINVAL);
        if (req->newptr == NULL)
                return (EPERM);
        if (req->newlen < sizeof(addrs))
                return (ENOMEM);
        error = SYSCTL_IN(req, &addrs, sizeof(addrs));
        if (error)
                return (error);

        switch (addrs[0].ss_family) {
#ifdef INET6
        case AF_INET6:
                fin6 = (struct sockaddr_in6 *)&addrs[0];
                lin6 = (struct sockaddr_in6 *)&addrs[1];
                if (fin6->sin6_len != sizeof(struct sockaddr_in6) ||
                    lin6->sin6_len != sizeof(struct sockaddr_in6))
                        return (EINVAL);
                if (IN6_IS_ADDR_V4MAPPED(&fin6->sin6_addr)) {
                        if (!IN6_IS_ADDR_V4MAPPED(&lin6->sin6_addr))
                                return (EINVAL);
                        in6_sin6_2_sin_in_sock((struct sockaddr *)&addrs[0]);
                        in6_sin6_2_sin_in_sock((struct sockaddr *)&addrs[1]);
#ifdef INET
                        fin = (struct sockaddr_in *)&addrs[0];
                        lin = (struct sockaddr_in *)&addrs[1];
#endif
                        break;
                }
                error = sa6_embedscope(fin6, V_ip6_use_defzone);
                if (error)
                        return (error);
                error = sa6_embedscope(lin6, V_ip6_use_defzone);
                if (error)
                        return (error);
                break;
#endif
#ifdef INET
        case AF_INET:
                fin = (struct sockaddr_in *)&addrs[0];
                lin = (struct sockaddr_in *)&addrs[1];
                if (fin->sin_len != sizeof(struct sockaddr_in) ||
                    lin->sin_len != sizeof(struct sockaddr_in))
                        return (EINVAL);
                break;
#endif
        default:
                return (EINVAL);
        }
        NET_EPOCH_ENTER(et);
        switch (addrs[0].ss_family) {
#ifdef INET6
        case AF_INET6:
                inp = in6_pcblookup(&V_tcbinfo, &fin6->sin6_addr,
                    fin6->sin6_port, &lin6->sin6_addr, lin6->sin6_port,
                    INPLOOKUP_WLOCKPCB, NULL);
                break;
#endif
#ifdef INET
        case AF_INET:
                inp = in_pcblookup(&V_tcbinfo, fin->sin_addr, fin->sin_port,
                    lin->sin_addr, lin->sin_port, INPLOOKUP_WLOCKPCB, NULL);
                break;
#endif
        }
        if (inp != NULL) {
                if (!SOLISTENING(inp->inp_socket)) {
                        tp = intotcpcb(inp);
                        tp = tcp_drop(tp, ECONNABORTED);
                        if (tp != NULL)
                                INP_WUNLOCK(inp);
                } else
                        INP_WUNLOCK(inp);
        } else
                error = ESRCH;
        NET_EPOCH_EXIT(et);
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, TCPCTL_DROP, drop,
    CTLFLAG_VNET | CTLTYPE_STRUCT | CTLFLAG_WR | CTLFLAG_SKIP |
    CTLFLAG_NEEDGIANT, NULL, 0, sysctl_drop, "",
    "Drop TCP connection");

static int
tcp_sysctl_setsockopt(SYSCTL_HANDLER_ARGS)
{
        return (sysctl_setsockopt(oidp, arg1, arg2, req, &V_tcbinfo,
            &tcp_ctloutput_set));
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, setsockopt,
    CTLFLAG_VNET | CTLTYPE_STRUCT | CTLFLAG_WR | CTLFLAG_SKIP |
    CTLFLAG_MPSAFE, NULL, 0, tcp_sysctl_setsockopt, "",
    "Set socket option for TCP endpoint");

#ifdef KERN_TLS
static int
sysctl_switch_tls(SYSCTL_HANDLER_ARGS)
{
        /* addrs[0] is a foreign socket, addrs[1] is a local one. */
        struct sockaddr_storage addrs[2];
        struct inpcb *inp;
#ifdef INET
        struct sockaddr_in *fin = NULL, *lin = NULL;
#endif
        struct epoch_tracker et;
#ifdef INET6
        struct sockaddr_in6 *fin6, *lin6;
#endif
        int error;

        inp = NULL;
#ifdef INET6
        fin6 = lin6 = NULL;
#endif
        error = 0;

        if (req->oldptr != NULL || req->oldlen != 0)
                return (EINVAL);
        if (req->newptr == NULL)
                return (EPERM);
        if (req->newlen < sizeof(addrs))
                return (ENOMEM);
        error = SYSCTL_IN(req, &addrs, sizeof(addrs));
        if (error)
                return (error);

        switch (addrs[0].ss_family) {
#ifdef INET6
        case AF_INET6:
                fin6 = (struct sockaddr_in6 *)&addrs[0];
                lin6 = (struct sockaddr_in6 *)&addrs[1];
                if (fin6->sin6_len != sizeof(struct sockaddr_in6) ||
                    lin6->sin6_len != sizeof(struct sockaddr_in6))
                        return (EINVAL);
                if (IN6_IS_ADDR_V4MAPPED(&fin6->sin6_addr)) {
                        if (!IN6_IS_ADDR_V4MAPPED(&lin6->sin6_addr))
                                return (EINVAL);
                        in6_sin6_2_sin_in_sock((struct sockaddr *)&addrs[0]);
                        in6_sin6_2_sin_in_sock((struct sockaddr *)&addrs[1]);
#ifdef INET
                        fin = (struct sockaddr_in *)&addrs[0];
                        lin = (struct sockaddr_in *)&addrs[1];
#endif
                        break;
                }
                error = sa6_embedscope(fin6, V_ip6_use_defzone);
                if (error)
                        return (error);
                error = sa6_embedscope(lin6, V_ip6_use_defzone);
                if (error)
                        return (error);
                break;
#endif
#ifdef INET
        case AF_INET:
                fin = (struct sockaddr_in *)&addrs[0];
                lin = (struct sockaddr_in *)&addrs[1];
                if (fin->sin_len != sizeof(struct sockaddr_in) ||
                    lin->sin_len != sizeof(struct sockaddr_in))
                        return (EINVAL);
                break;
#endif
        default:
                return (EINVAL);
        }
        NET_EPOCH_ENTER(et);
        switch (addrs[0].ss_family) {
#ifdef INET6
        case AF_INET6:
                inp = in6_pcblookup(&V_tcbinfo, &fin6->sin6_addr,
                    fin6->sin6_port, &lin6->sin6_addr, lin6->sin6_port,
                    INPLOOKUP_WLOCKPCB, NULL);
                break;
#endif
#ifdef INET
        case AF_INET:
                inp = in_pcblookup(&V_tcbinfo, fin->sin_addr, fin->sin_port,
                    lin->sin_addr, lin->sin_port, INPLOOKUP_WLOCKPCB, NULL);
                break;
#endif
        }
        NET_EPOCH_EXIT(et);
        if (inp != NULL) {
                struct socket *so;

                so = inp->inp_socket;
                soref(so);
                error = ktls_set_tx_mode(so,
                    arg2 == 0 ? TCP_TLS_MODE_SW : TCP_TLS_MODE_IFNET);
                INP_WUNLOCK(inp);
                sorele(so);
        } else
                error = ESRCH;
        return (error);
}

SYSCTL_PROC(_net_inet_tcp, OID_AUTO, switch_to_sw_tls,
    CTLFLAG_VNET | CTLTYPE_STRUCT | CTLFLAG_WR | CTLFLAG_SKIP |
    CTLFLAG_NEEDGIANT, NULL, 0, sysctl_switch_tls, "",
    "Switch TCP connection to SW TLS");
SYSCTL_PROC(_net_inet_tcp, OID_AUTO, switch_to_ifnet_tls,
    CTLFLAG_VNET | CTLTYPE_STRUCT | CTLFLAG_WR | CTLFLAG_SKIP |
    CTLFLAG_NEEDGIANT, NULL, 1, sysctl_switch_tls, "",
    "Switch TCP connection to ifnet TLS");
#endif

/*
 * Generate a standardized TCP log line for use throughout the
 * tcp subsystem.  Memory allocation is done with M_NOWAIT to
 * allow use in the interrupt context.
 *
 * NB: The caller MUST free(s, M_TCPLOG) the returned string.
 * NB: The function may return NULL if memory allocation failed.
 *
 * Due to header inclusion and ordering limitations the struct ip
 * and ip6_hdr pointers have to be passed as void pointers.
 */
char *
tcp_log_vain(struct in_conninfo *inc, struct tcphdr *th, const void *ip4hdr,
    const void *ip6hdr)
{

        /* Is logging enabled? */
        if (V_tcp_log_in_vain == 0)
                return (NULL);

        return (tcp_log_addr(inc, th, ip4hdr, ip6hdr));
}

char *
tcp_log_addrs(struct in_conninfo *inc, struct tcphdr *th, const void *ip4hdr,
    const void *ip6hdr)
{

        /* Is logging enabled? */
        if (tcp_log_debug == 0)
                return (NULL);

        return (tcp_log_addr(inc, th, ip4hdr, ip6hdr));
}

static char *
tcp_log_addr(struct in_conninfo *inc, struct tcphdr *th, const void *ip4hdr,
    const void *ip6hdr)
{
        char *s, *sp;
        size_t size;
#ifdef INET
        const struct ip *ip = (const struct ip *)ip4hdr;
#endif
#ifdef INET6
        const struct ip6_hdr *ip6 = (const struct ip6_hdr *)ip6hdr;
#endif /* INET6 */

        /*
         * The log line looks like this:
         * "TCP: [1.2.3.4]:50332 to [1.2.3.4]:80 tcpflags 0x2<SYN>"
         */
        size = sizeof("TCP: []:12345 to []:12345 tcpflags 0x2<>") +
            sizeof(PRINT_TH_FLAGS) + 1 +
#ifdef INET6
            2 * INET6_ADDRSTRLEN;
#else
            2 * INET_ADDRSTRLEN;
#endif /* INET6 */

        s = malloc(size, M_TCPLOG, M_ZERO|M_NOWAIT);
        if (s == NULL)
                return (NULL);

        strcat(s, "TCP: [");
        sp = s + strlen(s);

        if (inc && ((inc->inc_flags & INC_ISIPV6) == 0)) {
                inet_ntoa_r(inc->inc_faddr, sp);
                sp = s + strlen(s);
                sprintf(sp, "]:%i to [", ntohs(inc->inc_fport));
                sp = s + strlen(s);
                inet_ntoa_r(inc->inc_laddr, sp);
                sp = s + strlen(s);
                sprintf(sp, "]:%i", ntohs(inc->inc_lport));
#ifdef INET6
        } else if (inc) {
                ip6_sprintf(sp, &inc->inc6_faddr);
                sp = s + strlen(s);
                sprintf(sp, "]:%i to [", ntohs(inc->inc_fport));
                sp = s + strlen(s);
                ip6_sprintf(sp, &inc->inc6_laddr);
                sp = s + strlen(s);
                sprintf(sp, "]:%i", ntohs(inc->inc_lport));
        } else if (ip6 && th) {
                ip6_sprintf(sp, &ip6->ip6_src);
                sp = s + strlen(s);
                sprintf(sp, "]:%i to [", ntohs(th->th_sport));
                sp = s + strlen(s);
                ip6_sprintf(sp, &ip6->ip6_dst);
                sp = s + strlen(s);
                sprintf(sp, "]:%i", ntohs(th->th_dport));
#endif /* INET6 */
#ifdef INET
        } else if (ip && th) {
                inet_ntoa_r(ip->ip_src, sp);
                sp = s + strlen(s);
                sprintf(sp, "]:%i to [", ntohs(th->th_sport));
                sp = s + strlen(s);
                inet_ntoa_r(ip->ip_dst, sp);
                sp = s + strlen(s);
                sprintf(sp, "]:%i", ntohs(th->th_dport));
#endif /* INET */
        } else {
                free(s, M_TCPLOG);
                return (NULL);
        }
        sp = s + strlen(s);
        if (th)
                sprintf(sp, " tcpflags 0x%b", tcp_get_flags(th), PRINT_TH_FLAGS);
        if (*(s + size - 1) != '\0')
                panic("%s: string too long", __func__);
        return (s);
}

/*
 * A subroutine which makes it easy to track TCP state changes with DTrace.
 * This function shouldn't be called for t_state initializations that don't
 * correspond to actual TCP state transitions.
 */
void
tcp_state_change(struct tcpcb *tp, int newstate)
{
#if defined(KDTRACE_HOOKS)
        int pstate = tp->t_state;
#endif

        TCPSTATES_DEC(tp->t_state);
        TCPSTATES_INC(newstate);
        tp->t_state = newstate;
        TCP_PROBE6(state__change, NULL, tp, NULL, tp, NULL, pstate);
}

/*
 * Create an external-format (``xtcpcb'') structure using the information in
 * the kernel-format tcpcb structure pointed to by tp.  This is done to
 * reduce the spew of irrelevant information over this interface, to isolate
 * user code from changes in the kernel structure, and potentially to provide
 * information-hiding if we decide that some of this information should be
 * hidden from users.
 */
void
tcp_inptoxtp(const struct inpcb *inp, struct xtcpcb *xt)
{
        struct tcpcb *tp = intotcpcb(inp);
        sbintime_t now;

        bzero(xt, sizeof(*xt));
        xt->t_state = tp->t_state;
        xt->t_logstate = tp->t_logstate;
        xt->t_flags = tp->t_flags;
        xt->t_sndzerowin = tp->t_sndzerowin;
        xt->t_sndrexmitpack = tp->t_sndrexmitpack;
        xt->t_rcvoopack = tp->t_rcvoopack;
        xt->t_rcv_wnd = tp->rcv_wnd;
        xt->t_snd_wnd = tp->snd_wnd;
        xt->t_snd_cwnd = tp->snd_cwnd;
        xt->t_snd_ssthresh = tp->snd_ssthresh;
        xt->t_dsack_bytes = tp->t_dsack_bytes;
        xt->t_dsack_tlp_bytes = tp->t_dsack_tlp_bytes;
        xt->t_dsack_pack = tp->t_dsack_pack;
        xt->t_maxseg = tp->t_maxseg;
        xt->xt_ecn = (tp->t_flags2 & TF2_ECN_PERMIT) ? 1 : 0 +
                     (tp->t_flags2 & TF2_ACE_PERMIT) ? 2 : 0;

        now = getsbinuptime();
#define COPYTIMER(which,where)  do {                                    \
        if (tp->t_timers[which] != SBT_MAX)                             \
                xt->where = (tp->t_timers[which] - now) / SBT_1MS;      \
        else                                                            \
                xt->where = 0;                                          \
} while (0)
        COPYTIMER(TT_DELACK, tt_delack);
        COPYTIMER(TT_REXMT, tt_rexmt);
        COPYTIMER(TT_PERSIST, tt_persist);
        COPYTIMER(TT_KEEP, tt_keep);
        COPYTIMER(TT_2MSL, tt_2msl);
#undef COPYTIMER
        xt->t_rcvtime = 1000 * (ticks - tp->t_rcvtime) / hz;

        xt->xt_encaps_port = tp->t_port;
        bcopy(tp->t_fb->tfb_tcp_block_name, xt->xt_stack,
            TCP_FUNCTION_NAME_LEN_MAX);
        bcopy(CC_ALGO(tp)->name, xt->xt_cc, TCP_CA_NAME_MAX);
#ifdef TCP_BLACKBOX
        (void)tcp_log_get_id(tp, xt->xt_logid);
#endif

        xt->xt_len = sizeof(struct xtcpcb);
        in_pcbtoxinpcb(inp, &xt->xt_inp);
}

void
tcp_log_end_status(struct tcpcb *tp, uint8_t status)
{
        uint32_t bit, i;

        if ((tp == NULL) ||
            (status > TCP_EI_STATUS_MAX_VALUE) ||
            (status == 0)) {
                /* Invalid */
                return;
        }
        if (status > (sizeof(uint32_t) * 8)) {
                /* Should this be a KASSERT? */
                return;
        }
        bit = 1U << (status - 1);
        if (bit & tp->t_end_info_status) {
                /* already logged */
                return;
        }
        for (i = 0; i < TCP_END_BYTE_INFO; i++) {
                if (tp->t_end_info_bytes[i] == TCP_EI_EMPTY_SLOT) {
                        tp->t_end_info_bytes[i] = status;
                        tp->t_end_info_status |= bit;
                        break;
                }
        }
}

int
tcp_can_enable_pacing(void)
{

        if ((tcp_pacing_limit == -1) ||
            (tcp_pacing_limit > number_of_tcp_connections_pacing)) {
                atomic_fetchadd_int(&number_of_tcp_connections_pacing, 1);
                shadow_num_connections = number_of_tcp_connections_pacing;
                return (1);
        } else {
                return (0);
        }
}

static uint8_t tcp_pacing_warning = 0;

void
tcp_decrement_paced_conn(void)
{
        uint32_t ret;

        ret = atomic_fetchadd_int(&number_of_tcp_connections_pacing, -1);
        shadow_num_connections = number_of_tcp_connections_pacing;
        KASSERT(ret != 0, ("tcp_paced_connection_exits -1 would cause wrap?"));
        if (ret == 0) {
                if (tcp_pacing_limit != -1) {
                        printf("Warning all pacing is now disabled, count decrements invalidly!\n");
                        tcp_pacing_limit = 0;
                } else if (tcp_pacing_warning == 0) {
                        printf("Warning pacing count is invalid, invalid decrement\n");
                        tcp_pacing_warning = 1;
                }
        }
}